code: def test_duplicate_groupby_issues(self):
      idx_tp = [
          ("600809", "20061231"),
          ("600809", "20070331"),
          ("600809", "20070630"),
          ("600809", "20070331"),
      ]
      dt = ["demo", "demo", "demo", "demo"]
  
      idx = MultiIndex.from_tuples(idx_tp, names=["STK_ID", "RPT_Date"])
      s = Series(dt, index=idx)
  
      result = s.groupby(s.index).first()
      assert len(result) == 3
  
imports: import datetime
  import numpy
  import pytest
  import pandas
  from pandas import DataFrame, MultiIndex, Series
  import pandas._testing
label_desc: Use image node_id 14 for calling the TestMultiLevel obj's underlying member method code with example usage: obj.test_duplicate_groupby_issues() without return types