code: def to_file(self, path, mode="w"):
          
          with open(path, mode=mode) as f:
              for tree in self:
                  for label, line in tree.to_labeled_lines():
                      f.write(line + "\n")
docs: Save the corpus to a text file in the
          original format.
  
          Arguments:
          ----------
              path : str, where to save the corpus.
              mode : str, how to open the file.