ascentSiblings() {
    const results = new Array(TREE_SIZE_);
    for (let height = 0; height <= TREE_SIZE_; height++) {
      const masked = this.mask_(height);
      const bitToFlipDepth = TREE_SIZE_ - height - 1;
      masked[bitToFlipDepth >> 3] =
          masked[bitToFlipDepth >> 3] ^ MASKS_[bitToFlipDepth % 8];
      results[height] = new TreeIndex(masked);
    }
    return results;
  }
Returns an array of all the sibling nodes encountered when climbing the
tree from this leaf to the root.  Nodes above the leaf nodes have their
irrelevant bits masked.

@return {!Array<!TreeIndex>}