Have your characters ascend the ladder, but be careful at the top because enemies are waiting. Now drop back down and head right to the ladder. Dig it up and you'll send little creatures scurrying toward the lower right, where they'll provide a ladder so that they can climb the steep embankment and flee in that direction. As Fang, climb up the ladder and head in that direction. A ladder will drop down that you can climb toward the upper left. Use Wingardium Leviosa magic to assemble the pieces and form a cloud that will water the tree.
Behind that spot, there's a collection of circular LEGO discs and behind those a moving tree. Watch out for the nasty vines that grow around the area where you find Fang.