The tree below is an example of what you can do with PHP DBTreeView.
The content of this treeview is extractd from the NACEBEL codes of the belgian federal public service of economy. The content is in french (sorry...).
The treeview has more than 3800 nodes !
This useful tree download nodes on demand. When you clic on a '+' to see a branch, a request is sent to the server, without page refresh.