code: def _add_edus_to_tree(parented_tree, edus):
      
      for i, child in enumerate(parented_tree):
          if isinstance(child, nltk.Tree):
              _add_edus_to_tree(child, edus)
          else:
              edu_index = int(child)
              edu_tokens = edus[edu_index]
              parented_tree[i] = u" ".join(edu_tokens)
docs: replace EDU indices with the text of the EDUs
      in a parented tree.
  
      Parameters
      ----------
      parented_tree : nltk.ParentedTree
          a parented tree that only contains EDU indices
          as leaves
      edus : list(list(unicode))
          a list of EDUs, where each EDU is represented as
          a list of tokens