Answer: It sounds to me as though you have grown an avocado tree from a seed. Usually we recommend pinching off the top few leaves when the plant is about 12" tall so it will branch out. Then, when each stem reaches 8" long, pinch out the tops of those, too. When a tree has branches it will naturally develop a thick, sturdy trunk. It may not be too late for you to encourage branching in your tree. Start by pinching out the very tip of each branch. This will result in two new stems growing wherever you pinch. As your tree develops lots of branches the trunk should thicken up.
Best wishes with your avocado tree.
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