From the Super Mario Wiki
Tree Freak is a boss in the game Wario World on the Beanstalk Way level. Tree Freak is a massive oak tree with green leaves and spiky fruits growing on its branches. When Wario ground-pounds near the tree, it will shake the ground and cause the tree to drop its fruit. Wario must pick it up (on the un-spiked side) and chuck them at the tree's weak spot; a small bud on the front of the tree. One, two, or three hits will defeat it. Wario must fight Tree Freak three times during the level; once at the beginning, once in the middle and once at the end.