[Lizard]

This blob of code might also be helpful:

on copyChildTasks(sourceTree, destTree, destProject)
	using terms from application "OmniPlan"
		repeat with c in child tasks of sourceTree
			set newTask to my copyTask(c, destTree, destProject)
			my copyChildTasks(c, newTask, destProject)
		end repeat
	end using terms from
end copyChildTasks

and

set frontWindow to front window
set destDoc to document of frontWindow
set destProject to project of my destDoc
tell destProject
	set newProjectRoot to make new task with properties {name:sourceName, note:projnote}
end tell