code: def _calculate_children(self, column_name):
      children = self._split_column_value(column_name)
      children = self._change_no_children_value(children)
      nodes = self._get_column_value(self.NODE_COLUMN)
      return dict(zip(nodes, map(int, children)))
  
imports: import json
  import math
  from collections import defaultdict
  from typing import List, Mapping
  import numpy
  from dtreeviz.models.shadow_decision_tree import VisualisationNotYetSupportedError
  from dtreeviz.models.shadow_decision_tree import ShadowDecTree
  from dtreeviz import utils
  import xgboost
  from xgboost.core import Booster
label_desc: Use image node_id 21 for calling the ShadowXGBDTree obj's underlying member method code with example usage: obj._calculate_children(column_name) and returns: dict