code: def _add_bench_to_position(
      position_df: pd.DataFrame = None, bench: pd.Series = None
  ) -> pd.DataFrame:
      """Concat position with bench
  
      :param position_df: position DataFrame
      :param bench: report normal data
      :return: concat result
      """
      _temp_df = position_df.reset_index(level="instrument")
      # FIXME: After the stock is bought and sold, the rise and fall of the next trading day are calculated.
      _temp_df["bench"] = bench.shift(-1)
      res_df = _temp_df.set_index(["instrument", _temp_df.index])
      return res_df
  
imports: import pandas
  from ....backtest.profit_attribution import get_stock_weight_df
label_desc: Use image node_id 3 for calling a global function with example usage: _add_bench_to_position(position_df, bench) and returns: res_df