code: def kv_depth(d, depth, _counter=1):
          
          if depth == 0:
              yield d[_meta]["_rootname"], d
          else:
              if _counter == depth:
                  for key, node in DictTree.kv(d):
                      yield key, node
              else:
                  _counter += 1
                  for node in DictTree.v(d):
                      for key, node in DictTree.kv_depth(node, depth, _counter):
                          yield key, node
docs: Iterate items on specific depth.
          depth has to be greater equal than 0.
      
          Usage::
              
              >>> for key, node in DictTree.kv_depth(d, 2):
              >>>     print(key, DictTree.getattr(node, "population"))   
              bethesta 5800
              germentown 1400
              vienna 1500
              arlington 5000