code: def __iadd__(self, other):
      raise ValueError("%s may not be modified" % type(self).__name__)
  
imports: from nltk.probability import ProbabilisticMixIn
  from nltk.tree.parented import MultiParentedTree, ParentedTree
  from nltk.tree.tree import Tree
label_desc: Use image node_id 6 for calling the ImmutableTree obj's underlying member method code with example usage: obj.__iadd__(other) without return types