Method _getLevel

src/cdk/tree/tree.ts:839–841

* For the given node, determine the level where this node appears in the tree. * * This is intended to be used for `aria-level` but is 0-indexed.

(node: T)

   * This is intended to be used for `aria-level` but is 0-indexed.
   */
  _getLevel(node: T) {
    return this._levels.get(this._getExpansionKey(node));
  }

  /**
   * For the given node, determine the size of the parent's child set.