code: def add_child(self, feature_val, child):
      self._mapping[feature_val] = len(self.children)
      self._r_mapping[len(self.children)] = feature_val
      self.children.append(child)
  
imports: from __future__ import annotations
  import abc
  import math
  from ..base import Branch
label_desc: Use image node_id 5 for calling the NominalMultiwayBranch obj's underlying member method code with example usage: obj.add_child(feature_val, child) without return types