code: def set_root(self, depth, index):
          
          if depth < len(self._levels):
              self._levels[depth].set_root(index)
docs: Set the level\'s root of the given depth to index
  
          :param depth: the depth level
          :type depth: int
          :param index: the new root index
          :type index: QtCore.QModelIndex
          :returns: None
          :rtype: None
          :raises: None