Method _getSetSize

src/cdk/tree/tree.ts:848–851

* For the given node, determine the size of the parent's child set. * * This is intended to be used for `aria-setsize`.

(dataNode: T)

   * This is intended to be used for `aria-setsize`.
   */
  _getSetSize(dataNode: T) {
    const set = this._getAriaSet(dataNode);
    return set.length;
  }

  /**
   * For the given node, determine the index (starting from 1) of the node in its parent's child set.