title: Angular Material mat-tree with checkboxes select all
body: <p>I'm using <a href="https://stackblitz.com/angular/gabkadkvybq?file=app%2Ftree-checklist-example.html" rel="nofollow noreferrer">Tree with checkboxes</a>, and I want to add a button to check all checkboxes, I tried different methods but no good, the best thing i was able to achieve is this:</p>
  
  <pre><code>  selectAllFiscal() {
      this.rootItems.forEach(node =&gt; {
        this.todoItemSelectionToggle(node);
      });
    }
  </code></pre>
  
  <p>rootItems is an array of root nodes.</p>
  
  <p>I can see that nodes are selected when I iterate <code>checklistSelection.selected</code>, but the checkboxes are not selected in the browser, can anybody point the problem, thanks.</p>