diff --git a/src/index.ts b/src/index.ts
index 6c4761a..9e12573 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -9,4 +9,5 @@ export * from './lib/utils/types/tooltip-positions.type';
 export * from './lib/filtering/filter.service';
 export * from './lib/filtering/filter-utils';
 export * from './lib/filtering/models/filter-group.model';
+export * from './lib/filtering/models/nested-filter.model';
 export * from './lib/filtering/models/filter.model';
diff --git a/src/lib/filtering/filter-utils.ts b/src/lib/filtering/filter-utils.ts
index 9693860..90aeddc 100644
--- a/src/lib/filtering/filter-utils.ts
+++ b/src/lib/filtering/filter-utils.ts
@@ -1,7 +1,8 @@
-import { FilterModel } from './models/filter.model';
+import { NestedFilter } from './models/nested-filter.model';
 import { FilterGroup } from './models/filter-group.model';
+import { Filter } from './models/filter.model';
 
-export function processFilters(oldFilters: FilterModel[], newFilters: FilterModel[]) {
+export function processFilters(oldFilters: NestedFilter[], newFilters: NestedFilter[]) {
     copySettings(oldFilters, newFilters);
     if (newFilters) {
         newFilters.forEach(filter => {
@@ -11,33 +12,33 @@ export function processFilters(oldFilters: FilterModel[], newFilters: FilterMode
     return newFilters;
 }
 
-function copySettings(oldFilters: FilterModel[], newFilters: FilterModel[]) {
+function copySettings(oldFilters: NestedFilter[], newFilters: NestedFilter[]) {
     if (oldFilters && newFilters) {
         for (const oldFilter of oldFilters) {
             const newFilter = newFilters.find(f => f.key === oldFilter.key);
             if (newFilter) {
                 newFilter.checked = oldFilter.checked;
                 newFilter.indeterminate = oldFilter.indeterminate;
-                if (oldFilter.filters && newFilter.filters) copySettings(oldFilter.filters, newFilter.filters);
+                if (oldFilter.children && newFilter.children) copySettings(oldFilter.children, newFilter.children);
             }
         }
     }
 }
 
-export function handleCheckedValue(filter: FilterModel) {
-    if (filter.filters && filter.filters.length) {
-        filter.checked = filter.filters.reduce<boolean>((acc, next) => acc && !!next.checked, true);
+export function handleCheckedValue(filter: NestedFilter) {
+    if (filter.children && filter.children.length) {
+        filter.checked = filter.children.reduce<boolean>((acc, next) => acc && !!next.checked, true);
         if (filter.checked) {
             filter.indeterminate = false;
         } else {
-            filter.indeterminate = filter.filters.reduce<boolean>((acc, next) => acc || !!next.checked, false);
+            filter.indeterminate = filter.children.reduce<boolean>((acc, next) => acc || !!next.checked, false);
         }
     } else {
         filter.indeterminate = false;
     }
 }
 
-export function checkFilter(entity: any, filters: FilterModel[], validate: Function, validateArgs: any = [], matchAll: boolean = false) {
+export function checkFilter(entity: any, filters: NestedFilter[], validate: Function, validateArgs: any = [], matchAll: boolean = false) {
     const hasChecked = filters.find(f => f.checked);
 
     if (validateArgs) {
@@ -65,7 +66,7 @@ export function checkFilter(entity: any, filters: FilterModel[], validate: Funct
     return filterMatched;
 }
 
-export const keyChecker = (key: string) => (entity: any, filter: FilterModel) => entity[key] === filter.key;
+export const keyChecker = (key: string) => (entity: any, filter: NestedFilter) => entity[key] === filter.key;
 
 export function getFilteredEntities<T>(entities: T[], filters: FilterGroup[]) {
     const filteredEntities: T[] = [];
@@ -80,3 +81,11 @@ export function getFilteredEntities<T>(entities: T[], filters: FilterGroup[]) {
     }
     return filteredEntities;
 }
+
+export function flatChildren(filters: NestedFilter[]): Filter[] {
+    return filters.reduce((acc: Filter[], f) => [...acc, ...(f?.children ?? [])], []);
+}
+
+export function toFlatFilters(groups: FilterGroup[]): Filter[] {
+    return groups.reduce((acc: Filter[], f) => [...acc, ...f.filters, ...flatChildren(f.filters)], []);
+}
diff --git a/src/lib/filtering/filter.service.ts b/src/lib/filtering/filter.service.ts
index 1ebff7d..5c90d8f 100644
--- a/src/lib/filtering/filter.service.ts
+++ b/src/lib/filtering/filter.service.ts
@@ -1,9 +1,9 @@
 import { Injectable } from '@angular/core';
-import { processFilters } from './filter-utils';
+import { processFilters, toFlatFilters } from './filter-utils';
 import { BehaviorSubject, Observable, Subject } from 'rxjs';
 import { distinctUntilChanged, map, startWith, switchMap } from 'rxjs/operators';
 import { FilterGroup } from './models/filter-group.model';
-import { FilterModel } from './models/filter.model';
+import { NestedFilter } from './models/nested-filter.model';
 
 @Injectable()
 export class FilterService {
@@ -21,7 +21,7 @@ export class FilterService {
 
     private get _showResetFilters$(): Observable<boolean> {
         return this.filterGroups$.pipe(
-            map(all => this._toFlatFilters(all)),
+            map(toFlatFilters),
             map(f => !!f.find(el => el.checked)),
             distinctUntilChanged()
         );
@@ -36,7 +36,7 @@ export class FilterService {
         if (!filters) return console.error(`Cannot find filter group "${filterGroupSlug}"`);
 
         let found = filters.find(f => f.key === key);
-        if (!found) found = filters.map(f => f.filters?.find(ff => ff.key === key))[0];
+        if (!found) found = filters.map(f => f.children?.find(ff => ff.key === key))[0];
         if (!found) return console.error(`Cannot find filter with key "${key}" in group "${filterGroupSlug}"`);
 
         found.checked = !found.checked;
@@ -56,7 +56,7 @@ export class FilterService {
         return this.filterGroups.find(group => group.slug === slug);
     }
 
-    getFilterModels$(filterGroupSlug: string): Observable<FilterModel[] | undefined> {
+    getFilterModels$(filterGroupSlug: string): Observable<NestedFilter[] | undefined> {
         return this.getFilterGroup$(filterGroupSlug).pipe(map(f => f?.filters));
     }
 
@@ -65,24 +65,14 @@ export class FilterService {
     }
 
     reset(): void {
-        this.filterGroups.forEach(item => {
-            item.filters.forEach(child => {
-                child.checked = false;
-                child.indeterminate = false;
-                child.filters?.forEach(f => {
-                    f.checked = false;
-                    f.indeterminate = false;
-                });
+        this.filterGroups.forEach(group => {
+            group.filters.forEach(filter => {
+                filter.checked = false;
+                filter.indeterminate = false;
+                filter.children?.forEach(f => (f.checked = false));
             });
         });
 
         this.refresh();
     }
-
-    private _toFlatFilters(entities: FilterGroup[]): FilterModel[] {
-        const flatChildren = (filters: FilterModel[]) =>
-            (filters ?? []).reduce((acc: FilterModel[], f) => [...acc, ...(f?.filters ?? [])], []);
-
-        return entities.reduce((acc: FilterModel[], f) => [...acc, ...f.filters, ...flatChildren(f.filters)], []);
-    }
 }
diff --git a/src/lib/filtering/models/filter-group.model.ts b/src/lib/filtering/models/filter-group.model.ts
index 7309ac4..ab1e50e 100644
--- a/src/lib/filtering/models/filter-group.model.ts
+++ b/src/lib/filtering/models/filter-group.model.ts
@@ -1,8 +1,8 @@
-import { FilterModel } from './filter.model';
+import { NestedFilter } from './nested-filter.model';
 import { TemplateRef } from '@angular/core';
 
 export interface FilterGroup {
-    filters: FilterModel[];
+    filters: NestedFilter[];
     readonly slug: string;
     readonly label?: string;
     readonly icon?: string;
diff --git a/src/lib/filtering/models/filter.model.ts b/src/lib/filtering/models/filter.model.ts
index f015950..a7a6dc6 100644
--- a/src/lib/filtering/models/filter.model.ts
+++ b/src/lib/filtering/models/filter.model.ts
@@ -1,13 +1,10 @@
-export interface FilterModel {
+export interface Filter {
     readonly key: string;
     checked?: boolean;
-    indeterminate?: boolean;
-    expanded?: boolean;
     matches?: number;
-    readonly label?: string;
+    readonly label: string;
     readonly icon?: string;
     readonly topLevelFilter?: boolean;
-    readonly filters?: FilterModel[];
     readonly checker?: (obj?: unknown) => boolean;
     readonly required?: boolean;
 }
diff --git a/src/lib/filtering/models/nested-filter.model.ts b/src/lib/filtering/models/nested-filter.model.ts
new file mode 100644
index 0000000..d553c17
--- /dev/null
+++ b/src/lib/filtering/models/nested-filter.model.ts
@@ -0,0 +1,7 @@
+import { Filter } from './filter.model';
+
+export interface NestedFilter extends Filter {
+    expanded?: boolean;
+    indeterminate?: boolean;
+    readonly children?: Filter[];
+}
diff --git a/tsconfig.lib.json b/tsconfig.lib.json
index bbcc12b..7136ec9 100644
--- a/tsconfig.lib.json
+++ b/tsconfig.lib.json
@@ -6,6 +6,7 @@
     "declaration": true,
     "declarationMap": true,
     "inlineSources": true,
+    "strict": true,
     "types": [],
     "lib": ["dom", "es2018"]
   },