Method toggleDescendants

src/cdk/tree/tree.ts:668–678

* If the data node is currently expanded, collapse it and all its descendants. * Otherwise, expand it and all its descendants.

(dataNode: T)

   * Otherwise, expand it and all its descendants.
   */
  toggleDescendants(dataNode: T): void {
    if (this.treeControl) {
      this.treeControl.toggleDescendants(dataNode);
    } else if (this._expansionModel) {
      if (this.isExpanded(dataNode)) {
        this.collapseDescendants(dataNode);
      } else {
        this.expandDescendants(dataNode);
      }
    }
  }

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