https://soooprmx.com/%ec%9d%b4%ec%a7%84%ed%83%90%ec%83%89%ed%8a%b8%eb%a6%ac-binary-search-tree%ec%97%90-%eb%8c%80%ed%95%b4-python/
이진탐색트리 (Binary Search Tree) 구현하기 - python