code: def tree_handler(*args, **kwargs):
      
      global _TREE_HANDLER
  
      if not _TREE_HANDLER:
          _TREE_HANDLER = TreeHandler(*args, **kwargs)
  
      return _TREE_HANDLER
docs: Singleton `TreeHandler` generator. Any arguments are given to
      :class:`TreeHandler`, when it is first created.
  
      Returns:
          obj: :class:`TreeHandler` instance.