This example demonstrates using the jQuery treeTable plugin (http://plugins.jquery.com/treetable) for an AJAX enabled tree. It uses Ruby on Rails and SQLite for the server side.
The file app/views/nodes/index.html.erb contains the interesting Javascript bits. It uses the jQuery.ajax function to download remote nodes when a node is expanded. It also uses jQuery.ajax to update the remote tree when a node is moved between branches (D&D).
This assusmes you already have Ruby and the bundler gem installed.
cd jquery-treetable-ajax-example
bundle install
bundle exec rake db:create
bundle exec rake db:migrate
bundle exec rake db:seed
script/rails server
Now open your browser at http://localhost:3000.