Sad avocado plant
I have a question about growing an avocado from seed. In the first picture there is my avocado tree planted last year in April, and this winter I had to bring the baby plant at home because the winter in my country is below 0 degrees Celsius. When I moved the plant home, all its leaves have fallen and now I'm not sure if my avocado tree is alive. In the second picture is the current condition of my plant. Can you tell me if my tree is alive and give me some advice what to do with my plant?
Unfortunately, I cannot tell whether your tree is alive from the pictures you sent. More importantly, avocados do not come true from seed. Whatever tree the seed produces may be of very poor quality. In the long run, your best bet is to purchase a grafted tree. The best variety to grow will depend upon your location.
However, it does appear a little dark in the photos, and the quality and amount of light may have some impact on the defoliation of your tree.
In what country are you trying to grow your avocado? Knowing this may help me better answer your question.
Here is a link to a Texas AgriLife Extension publication on avocados: Avocados
In general, avocados are a tropical evergreen, and cold is the biggest threat to their success. They will drop their leaves occasionally but will usually develop new ones very soon afterward. Also, avocados prefer well-drained soils.