Need a bit of anti-aliasing for the round shapes :)

Right :)

 

I wonder how it will look with a long method: they usually have rather flat ASTs that would result in a wide diagram.

Yes it will be pretty huge. However, 1) there is an option to scale the tree (nodes) 2) most of the methods should not be very long ;)
Still the problem remains.

I built it rather for fun and my possible future work, than for wide usage. But I think it may be nice for some people to one-click and see the tree, and play with it.

About GT inspector: yes I've seen the ast view in inspecotr, and it's amazing how many things we can do with it.