acts_as_tree

where I can add a patch to acts_as_tree plugin?

I'm not positive, but I think you'd fork the repo here:

http://github.com/rails/acts_as_tree/tree/master

...make a patch according to the basic idea behind these guidelines:

http://rails.lighthouseapp.com/projects/8994/sending-patches

...and create a ticket with your patch here:

http://rails.lighthouseapp.com/projects/8995-rails-plugins

- Trevor