How to make the content of list (tree view data in list ul and li tags) expanded by default?

In Html 

<ul style="list-style: none; Isexpanded:true" >

<li *ngFor="let contentNode of contentNodes" class="tree__branch" [ngClass]="{'tree__branch--has-children': contentNode.has_children}">

<a *ngIf="contentNode.has_children" (click)="contentNode.toggle=!contentNode.toggle" class="toggle">{{ !!contentNode.toggle ? '▼' : '▶' }}</a> <a [routerLink]="['/loc-admin/locationView', contentNode.pk_location_id]">📁</a>{{ contentNode.locationname }}

  <content-list *ngIf="contentNode.toggle" [startingNode]="contentNode.pk_location_id"  [myData]="rows"></content-list>

</li>

</ul>

In component.ts

export class ContentListComponent implements OnInit {

constructor (private _contentService: LocationService) {}

errorMessage: string;

@Input('startingNode')

private _startNodeId: string;

@Input('myData')

  private _myData = [];

rows=[];

  contentNodes: Location[];

  bookFilteredList : Location[];

ngOnInit() { 

this.rows=this._myData;

this.contentNodes=this.rows;

//console.dir(this.contentNodes);

//this.getContentNodes();

this.filter();

}

filter(){

//console.log('Excecute filter');

let storageId = this._startNodeId;

this.bookFilteredList = this.contentNodes.filter((book: Location) => book.parent_location_id === storageId);

this.contentNodes = this.bookFilteredList;

console.log(this.bookFilteredList);

return this.contentNodes;

}

// getContentNodes() {

// this._contentService.getChildLocations(this._startNodeId)

// .subscribe(

// contentNodes => this.contentNodes = contentNodes,

// error =>  this.errorMessage = <any>error

// );

// console.dir(this.contentNodes)

// }

toggleBranch(branchId:number){

console.log('branchId: ' + branchId);

}

}