Horizontal scrollbar treeview in Tkinter

Question

I have some problems with the treeview of Tkinter and the horizontal scrollbar. The scroll bar does not seem to work. It looks like a Tk bug.

I can not post pictures or links, sorry.

When I click on the branches to expand, the scrollbar does not work.

from Tkinter import *
import ttk


root = Tk()     

frame = Frame(root)

tree = ttk.Treeview(frame, selectmode='browse')

scrollbar_horizontal = ttk.Scrollbar(frame, orient='horizontal', command = tree.xview)    
scrollbar_vertical = ttk.Scrollbar(frame, orient='vertical', command = tree.yview)   
scrollbar_horizontal.pack(side='bottom', fill=X)    
scrollbar_vertical.pack(side='right', fill=Y)

tree.configure(xscrollcommand=scrollbar_horizontal.set, yscrollcommand=scrollbar_vertical.set)

tree.pack(side=LEFT, fill=BOTH, expand=False)

frame.pack(expand=False)

tree.insert('', '0', 'it_titulo', text='Matematicas')    
tree.insert('', '1', 'it_aritmetica', text='Aritmetica')    
tree.insert('', '2', 'it_algebra', text='Algebra')    
tree.insert('', 'end', 'it_geometria', text='Geometria')

tree.insert('it_aritmetica', '0', 'prop_sum', text='Propiedades de la suma')    
tree.insert('it_aritmetica', '1', 'prop_res', text='Propiedades de la resta')    
tree.insert('it_aritmetica', '2', 'prop_mul', text='Propiedades de la multiplicacion')    
tree.insert('it_aritmetica', '3', 'prop_div', text='Propiedades de la division')   
tree.insert('it_aritmetica', 'end', 'art_repaso', text='Repaso')    

tree.insert('it_algebra', '0', 'alg_ele', text='Algebra Elemental')    
tree.insert('it_algebra', '1', 'alg_int', text='Algebra Intermedia')    
tree.insert('it_algebra', '2', 'alg_avz', text='Algebra Avanzada')    
tree.insert('it_algebra', 'end', 'alg_repaso', text='Repaso')    

tree.insert('alg_ele', '0', 'prop_conm_adn', text='Propiedad conmutativa de la adicion')

root.mainloop()