There is a Javascript based thingie that works quite well and uses a cookie to manage the state of the tree. This should give you some ideas. You can get a version of it I worked on some time ago. Sorry about the broken images.

Another good start is to look at the javax.swing.tree package, and port that interface. This has a nice model/view/controller approach that you can use.

Christian Lemburg
Brainbench MVP for Perl
http://www.brainbench.com