docs: def map_indices_child2root(child, child_indices):
      """Map RTDC_Hierarchy event indices to root RTDCBase
  
      Parameters
      ----------
      child: RTDC_Hierarchy
          RTDCBase hierarchy child
      child_indices: 1d ndarray
          child indices to map
  
      Returns
      -------
      root_indices: 1d ndarray
          hierarchy root indices
          (not necessarily the indices of `parent`)
      """
      while True:
          indices = map_indices_child2parent(child=child,
                                             child_indices=child_indices)
          if isinstance(child.hparent, RTDC_Hierarchy):
              child = child.hparent
              child_indices = indices
          else:
              break
      return indices