Have you ever looked out of the window on a windy day and noticed that only the tops of the trees are shaking? The answer is most likely yes but you probably haven't thought of why this happens. The wind in general applies a force on the tree witch is what causes the tree to move, however, the tree can withstand some force and keep sturdy. As the force of the wind is applied further and further up the tree, the torque in being increased because the length of the "lever arm" is being increased. The maximum torque at the very top of the tree passes the threshold force that the tree can withstand and causes motion at the top of the tree!