How to define if component nested to itself in Angular 6?

<radio-ng-model-example>
    <md-radio-group class="example-radio-group" [(ngModel)]="favoriteSeason">
        <md-radio-button class="example-radio-button" *ngFor="let season of seasons" [value]="season">
            {{season}}
        </md-radio-button>
    </md-radio-group>
    <div class="example-selected-value">Your favorite season is: {{favoriteSeason}}</div>
</radio-ng-model-example>

@Input() assetId: string;

<asset assetId="x"></asset>

@Input() assetId: string;

<document [assetId]="assetId"></document>

export class AssetComponent {
  @ViewChild(DocumentComponent) document: DocumentComponent;
  @Input() set assetId(assetId) {
    this._assetId = assetId;
    this.document.assetId = assetId;
  } 

  get assetId() {
    return this._assetId;
  }

  private _assetId: string;
}

      <item
        *ngFor="let subItem of item.Children; trackBy: trackById"
        [item]="subItem">
      </item>

  trackById = (item) => item.Id;