Launch A Userform During Startup

I am trying to launch the userforms with the below codes during startup(that is when you click the excel file, the userform will automatically pop up).
Please, Can somebody guide me through ?
Compare_Map is a subroutine which is to be called when optionbutton3 is being selected.

Private Sub OptionButton1_Click()

End Sub

Private Sub OptionButton2_Click()

End Sub

Private Sub OptionButton3_Click()
Call Compare_Map
Exit Sub
End Sub