Twitter for iPad’s UI is so great. It uses very efficient and elegant method to show hierarchical information.
If you want to implement this in your app, there’s a good news. Check the following screen. Isn’t look similar to the twitter’s interface?
You can download source code from here: https://github.com/aaronbrethorst/StackScrollView
It’s still need some improvement to be elegant as twitter’s, but way the UI working is very similar.