code: def root(self):
      return None if self._root_id is None else self.nodes[self.root_id]
  
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  from turicreate.util import _raise_error_if_not_of_type
  from turicreate.toolkits._internal_utils import _numeric_param_check_range
  import sys
label_desc: Use image node_id 9 for calling the DecisionTree obj's underlying member method code with example usage: obj.root() and returns: unknown