code: def test_sorted_multiindex_after_union(self):
      # GH#44752
      midx = MultiIndex.from_product(
          [pd.date_range("20110101", periods=2), Index(["a", "b"])]
      )
      ser1 = Series(1, index=midx)
      ser2 = Series(1, index=midx[:2])
      df = pd.concat([ser1, ser2], axis=1)
      expected = df.copy()
      result = df.loc["2011-01-01":"2011-01-02"]
      tm.assert_frame_equal(result, expected)
  
      df = DataFrame({0: ser1, 1: ser2})
      result = df.loc["2011-01-01":"2011-01-02"]
      tm.assert_frame_equal(result, expected)
  
      df = pd.concat([ser1, ser2.reindex(ser1.index)], axis=1)
      result = df.loc["2011-01-01":"2011-01-02"]
      tm.assert_frame_equal(result, expected)
  
imports: import numpy
  import pytest
  from pandas.errors import IndexingError, PerformanceWarning
  import pandas
  from pandas import DataFrame, Index, MultiIndex, Series
  import pandas._testing
label_desc: Use image node_id 20 for calling the TestMultiIndexLoc obj's underlying member method code with example usage: obj.test_sorted_multiindex_after_union() without return types