open tooltip on start

How can I open a tooltip from ngboostrap when openeing the compnent.

I tried called the open method in the ngOnInit function but it didn't show it.

I tried the same method in a button click an that worked (based on the sample: https://ng-bootstrap.github.io/app/components/tooltip/demos/tplwithcontext/plnkr.html )

Code:

export class TooltipComponent implements OnInit {
    @ViewChild('tleft') public tooltip: NgbTooltip;

    ngOnInit() {
        this.tooltip.open();
    }
}

Template:

<p>
  <strong ngbTooltip="Tooltip on left" #tleft="ngbTooltip" triggers="manual">Tooltip is here</strong>?
</p>
<button type="button" class="btn btn-secondary" (click)="open()">
  Open
</button>