Tkinter question

[Ali Dada]

hi all:

i have a window made of a couple of buttons stacked above each other.i need to
any a widget on the top that opens a submenu to the right when clicked. how can
i do that? see the code below and tell me how to correct it (the submenu is
opening downwards over the other buttons, not to the right)

#!/usr/bin/env python
import sys
from Tkinter import *
from tkMessageBox import *
from tkSimpleDialog import askfloat


def makemenu(root):
    pref = Menu(root)
    root.config(menu=pref)

class Index(Frame):
	def __init__(self):
		Frame.__init__(self)
		self.pack()
		Button(self, text='Repository').pack(side=TOP, fill=BOTH)
		Button(self, text='Regression').pack(side=TOP, fill=BOTH)
		Button(self, text='Code Manage').pack(side=TOP, fill=BOTH)
		

	def makemenu(self, root):
		pref = Menu(root)
		root.config(menu=pref)
		pref1 = Menu(pref, tearoff=0)
		pref1.add_command(label='Cut', underline=0)
		pref1.add_command(label='Paste', underline=0)
		pref.add_cascade(label='Preference >',  menu=pref1,  underline=0)

if __name__ == '__main__':
	root=Tk()
	root.title('TAGZ')
	i = Index()
	i.makemenu(root)
	i.mainloop()