docs: def repr_tree(self):
          """
          reconstruct represented tree as a DiGraph to
          preserve the current rootedness
          """
          import utool as ut
          import networkx as nx
          repr_tree = nx.DiGraph()
          for u, v in ut.itertwo(self.values()):
              if not repr_tree.has_edge(v, u):
                  repr_tree.add_edge(u, v)
          return repr_tree