what wrong with this program?

[Ali]

The following program is supposed to display a dropdown menu, however,
it only shows the File and Help things.

from Tkinter import *

root = Tk()

#create menu
m = Menu(root)
root.config(menu=m)

filemenu = Menu(m)
m.add_cascade(label="File", menu="filemenu")
filemenu.add_command(label="New", command=callback)
filemenu.add_separator()
filemenu.add_command(label="Quit", command=callback)

helpmenu = Menu(m)
m.add_cascade(label="Help", menu="helpmenu")
helpmenu.add_command(label="About...", command=callback)

root.mainloop()

please help fix this program.