code: def _split_tree(layout):
      """Returns a tuple of two layouts, one containing the left
      subtree of the root vertex, and one containing the original tree
      with the left subtree removed."""
  
      one_found = False
      m = None
      for i in range(len(layout)):
          if layout[i] == 1:
              if one_found:
                  m = i
                  break
              else:
                  one_found = True
  
      if m is None:
          m = len(layout)
  
      left = [layout[i] - 1 for i in range(1, m)]
      rest = [0] + [layout[i] for i in range(m, len(layout))]
      return (left, rest)
  
file_path: networkx/networkx/generators/nonisomorphic_trees.py
imports: import networkx
label_desc: Use image node_id 5 for calling a global function with example usage: _split_tree(layout) and returns: left,  rest