After you are thorough with the theoretical concepts of binary tree and preparing all the interview questions, you can start practising coding questions starting from easy, then medium, and then finally hard level problems. You can start approaching topic wise questions, and then after becoming confident in those, you can do problems from mixed topics. There are tons of websites like GFG, LeetCode, which have quality questions to practice from. Practising enough varied problems will not only boost your confidence but will also help you ace your interviews.