code: def trees_to_dict(trees_list):
          
          result = {}
  
          for tree in trees_list:
              result.update(tree.to_dict())
  
          return result
docs: Convert a list of `TreeNode`s to an expansion dictionary.
  
          :param trees_list: A list of `TreeNode` instances
          :type trees_list: list[TreeNode]
  
          :return: An expansion dictionary that represents the expansions detailed in the provided expansions tree nodes
          :rtype: dict[union[str, unicode]]