I am doing a simple UI with TkInter in Python. I want a button at the top left, so I did something like 

```py
    back = Button(explorer, text="Back")
    back.pack(side="top", anchor="w")

```

where `explorer` is a frame, and I expected to see the button on top left, but it's stuck in the center. Any suggestions? I already tried to add `side=TOP` but it didn't work. What's the right way to do that?