Why does the following code not work, all it has to do is open a window with a small menu bar (Python)

Question

All this does is open a blank window with no menu, and the point of this was for me to make a menu

from tkinter import*
MainWindow = Tk()


def donothing():
    print("Ok, ok I won't...")



Topmenu = Menu(MainWindow)
MainWindow.config(menu=Topmenu)
Submenu = Menu(Topmenu)
Topmenu.add_cascade(label = "This does nothing.",menu = Submenu)
Submenu.add_command(label="This won't do anything.",command=donothing)
Submenu.add_command(label="Now...",command=donothing)
Submenu.add_separator()    
Submenu.add_command(label="Quit",command="Quit")



MainWindow.mainloop()