title: PrimeNG Treetable programmatically expand all nodes not working
body: <p>I'm trying to recursively expand all nodes on a Primeng TreeTable component but without success.
  The row icons change and nothing more happens, except when i manualy click on the expand/colapse icon and all nodes are expanded/collapsed accordingly.</p>
  <p>Here a stackbliz link for what i'm trying to do, <a href="https://stackblitz.com/edit/primeng-treetable-demo-nsvdr8" rel="nofollow noreferrer">Stackblitz code</a></p>
  <p>And this are my expand/colapse methods:</p>
  <pre><code>public expandAll(): void {
      this.files1.forEach(node =&gt; {
          this.expandCollapseRecursive(node, true);
      });
  }
  
  public collapseAll(): void {
      this.files1.forEach(node =&gt; {
          this.expandCollapseRecursive(node, false);
      });
  }
  
  private expandCollapseRecursive(node: TreeNode, isExpand: boolean): void {
      node.expanded = isExpand;
      if (node.children) {
          node.children.forEach(childNode =&gt; {
              this.expandCollapseRecursive(childNode, isExpand);
          });
      }
  }
  </code></pre>