My mom decided to cut the top of my avocado tree, it's about. The stem is now turning brown and withering where she cut it. I heard about cutting the top off to encourage growth of lower leaves/branches and keep the overall height lower, but I thought the top would slowly grow back, now it just looks like it's dieing. Is this normal? The tree/plant is 2.5 years old, not sure if there's anything else to mention about it.