I've just added a fully AJAX enabled editable tree on my demo site.
All modifications to the tree are transmitted to the database via an application process using AJAX.
Values are submitted using wwv_flow package variables:
g_x01 .. g_x10
The application process simply calls a database package, which references the wwv_flow package variables and updates the data.
The key to AJAX functionality in Oracle Apex is based around these "Global input variables for AJAX utilities".
This example has a fair bit going on, to see a simpler example check out:
- My demo using extJS
- Tyler Muths demo which uses jQuery