BSTFromPreOrder.java

class BSTFromPreOrder {
    public TreeNode bstFromPreorder(int[] preorder) {
        TreeNode root = null;
        for (int val : preorder) {
            root = insert(root, val);
        }
        return root;
    }
    private TreeNode insert(TreeNode node, int val) {
        if (node == null) {
            return new TreeNode(val);
        }
        if (val < node.val) {
            node.left = insert(node.left, val);
        } else {
            node.right = insert(node.right, val);
        }
        return node;
    }
}