Have you looked at wm_corecontrolstest application for tree table example? Default TaskSearchContentProvider which returns list of tasks needs to be repackaged into a com.webMethods.caf.faces.data.tree.object.ListTreeContentProvider which then used as input for a tree table.
As an alternative and possibly easier way would be to use Categorized Table control instead if Tree Table is all you need is some categorization of tasks, but without collapse/expand features of the tree. Then you can use TaskSearchProviders directly for this control. Again, please look at the wm_corecontrolstest for example for categorized table.
#webMethods-BPMS#webMethods#MWS-CAF-Task-Engine