code: def stats_on_depth(d, depth):
          
          root_nodes, leaf_nodes = 0, 0
          for _, node in DictTree.kv_depth(d, depth):
              if DictTree.length(node) == 0:
                  leaf_nodes += 1
              else:
                  root_nodes += 1
          total = root_nodes + leaf_nodes
          print("On depth %s, having %s root nodes, %s leaf nodes. "
                "%s nodes in total." % (depth, root_nodes, leaf_nodes, total))
docs: Display the node stats info on specific depth in this dict