Finding height in Binary Search Tree

The problem lies in your base case.

"The height of a tree is the length of the path from the root to the deepest node in the tree. A (rooted) tree with only a node (the root) has a height of zero." - Wikipedia

If there is no node, you want to return -1 not 0. This is because you are adding 1 at the end.

So if there isn't a node, you return -1 which cancels out the +1.

int findHeight(TreeNode<T> aNode) {
    if (aNode == null) {
        return -1;
    }

    int lefth = findHeight(aNode.left);
    int righth = findHeight(aNode.right);

    if (lefth > righth) {
        return lefth + 1;
    } else {
        return righth + 1;
    }
}

The height of a binary search tree is equal to number of layers - 1.

See the diagram at http://en.wikipedia.org/wiki/Binary_tree

Your recursion is good, so just subtract one at the root level.

Also note, you can clean up the function a bit by handling null nodes:

int findHeight(node) {
  if (node == null) return 0;
  return 1 + max(findHeight(node.left), findHeight(node.right));
}