Method expandDescendants

src/cdk/tree/tree.ts:683–695

* Expand the data node and all its descendants. If they are already expanded, does nothing.

(dataNode: T)

   * Expand the data node and all its descendants. If they are already expanded, does nothing.
   */
  expandDescendants(dataNode: T): void {
    if (this.treeControl) {
      this.treeControl.expandDescendants(dataNode);
    } else if (this._expansionModel) {
      const expansionModel = this._expansionModel;
      expansionModel.select(this._getExpansionKey(dataNode));
      this._getDescendants(dataNode)
        .pipe(take(1), takeUntil(this._onDestroy))
        .subscribe(children => {
          expansionModel.select(...children.map(child => this._getExpansionKey(child)));
        });
    }
  }

  /** Collapse the data node and all its descendants. If it is already collapsed, does nothing. */
  collapseDescendants(dataNode: T): void {