Multi-level tabs in Oracle Application Express (APEX) are notoriously difficult to work with - to the point that most developers avoid them all together. Lists, on the other hand, are both easy to work with and very flexible - even supporting multiple levels of nesting. The only trouble with lists is finding the right template as not all APEX themes contain a list template suitable for replacing tabs for navigation. Twitter Bootstrap to the rescue!
A multi-level navigation bar based on parts of Twitter Bootstrap
You will need to login in order to download a plugin. If you do not have an enkitec.com account, you can create one.