Give this a try...
Sub ShowOutlineLevel()
Const SUMMARY_LEVEL = 1
Const SECOND_LEVEL = 2
Const THIRD_LEVEL = 3
'ActiveSheet.Outline.ShowLevels RowLevels:=SUMMARY_LEVEL
'ActiveSheet.Outline.ShowLevels RowLevels:=SECOND_LEVEL
ActiveSheet.Outline.ShowLevels RowLevels:=THIRD_LEVEL
End Sub