code: function getBranchFromTree(tree, ary, index, i) {
    if (index == null) {
      index = null;
    }
    if (i == null) {
      i = 0;
    }
    if (index == null) {
      index = ary.length;
    }
    if (i === index) {
      return tree;
    }
    return getBranchFromTree(tree[ary[i]], ary, index, ++i);
  }
docs: Private