At the end of my presentation at KScope11, I received a couple of requests for a demonstration of how to use the tree region included in APEX to display bills of materials from the Oracle E-Business Suite (since I'd mentioned it as a possibility). That demo is now available here.
The nice thing about the APEX trees is that APEX builds the hierarchical SQL for you; you just have to get all the data you need for your tree into a single table or view. Because the EBS BOM data is spread across two tables, with item information in a third, a view is pretty much required.
The not-so-nice thing is that APEX includes an older version of jsTree, which doesn't have all of the features in the current version–most notably (to me, at least), the ability to use HTML in the titles of your tree nodes. It'd be really nice to make each level of the tree into a box that includes the item number, description, component quantity, and perhaps other information like the make/buy code, primary supplier information, lead times, onhand quantities, etc.
Since jsTree is still at a pre-1.0 release, I don't expect the newer version to be included in the upcoming 4.1 release. So if you want the newer features, you pretty much have to install the newer version yourself and build your own region. I'll see if I can knock that together over the upcoming week.