Two levels of items in an array list

Ionic Framework ionic-v3
1

Hi,

I have a array list of items:

  items = [
    {id: '1', title: 'item 1'},
    {id: '2', title: 'item 2'},
  ]

I want to add categories to this list and filter based on that, for example

-items
-- cat1
--- item 1
--- item 2
-- cat2
--- item 1
--- item 2
-- cat3
--- item 1
--- item 2

Also, how would I change the ngFor code to select the cat

<ion-list>
  <ion-item *ngFor="let item of items" (click)="clicked($event, item)">
    <h2>{{item.title}}</h2>
  </ion-item>
</ion-list>



  clicked (event, item){
    console.log(item.title);
  }