code: def compare_variables(tree_model, iter1, iter2, user_data=None):
          path1 = tree_model.get_path(iter1)[0]
          path2 = tree_model.get_path(iter2)[0]
          name1 = tree_model[path1][0]
          name2 = tree_model[path2][0]
          name1_as_bits = ' '.join(format(ord(x), 'b') for x in name1)
          name2_as_bits = ' '.join(format(ord(x), 'b') for x in name2)
          if name1_as_bits == name2_as_bits:
              return 0
          elif name1_as_bits > name2_as_bits:
              return 1
          else:
              return -1