text: import treeano
  import treeano.nodes as tn
  import canopy
  
  
  def create_big_node_graph(levels):
      assert levels >= 0
      if levels == 0:
          return tn.IdentityNode("i")
      else:
          prev = create_big_node_graph(levels - 1)
          return tn.SequentialNode(
              "s",
              [canopy.node_utils.suffix_node(prev, "0"),
               canopy.node_utils.suffix_node(prev, "1")])
  
  
  """
  20150808 results:
  
  %timeit create_big_node_graph(5)
  # cached_walk = True => 49.7ms
  # cached_walk = False => 254ms
  
  %timeit create_big_node_graph(10)
  # cached_walk = True => 1.77s
  # cached_walk = False => 16.5s
  """
  