Comment 6 for bug 351867

Unluckily I cannot provide you information about how to write a custom TreeModel. Nevertheless the link I posted above is a good start and I think you should really follow that path.

You should not just use the TreeModel for the TaskBrowser but as your general runtime-datastore. With the model at hand, TaskEditor and TaskBrowser can operate on the same data.

For example, when you open a TaskEditor and now drag'n'drop another task into the subtree of that task in the TaskBrowser, you will proparbly want to update both the TaskEditor and the Browser. You should be able to achieve this by the change-signals emitted by your model and propagated to both views.