I put button on a frame like this in Tkinter for python3:

```
b2_1 = Button(frame1, text='aaaaaaaaaaaa')
b2_1.pack(pady=20, side=RIGHT)

b2_2 = Button(frame1, text='bbbbbbbbbbbbbbb')
b2_2.pack()

```

I want the buttons b2\_1 and b2\_2 to be stick not only to the right side, but also to the bottom, one right above another. 
How can I do that?