What is the worst case time complexity of inserting n² elements into an AVL-tree with n elements initially?

The postorder traversal of a binary tree is $$8,9,6,7,4,5,2,3,1.$$ The inorder traversal of the same tree is $$8,6,9,4,7,2,5,1,3.$$ The height of a tree is the length of the longest path from the root to any leaf. The height of the binary tree above is ______.

Let $T$ be a binary search tree with 15 nodes. The minimum and maximum possible heights of $T$ are :

Note : The height of a tree with a single node is 0.

Consider a binary tree $$T$$ that has $$200$$ leaf nodes. Then, the number of nodes in $$T$$ that have exactly two children are ________.