code: def k_depth(d, depth, _counter=1):
          
          if depth == 0:
              yield d[_meta]["_rootname"]
          else:
              if _counter == depth:
                  for key in DictTree.k(d):
                      yield key
              else:
                  _counter += 1
                  for node in DictTree.v(d):
                      for key in DictTree.k_depth(node, depth, _counter):
                          yield key
docs: Iterate keys on specific depth.
          depth has to be greater equal than 0. 
          Usage reference see :meth:`DictTree.kv_depth()<DictTree.kv_depth>`