function BinarySearchTree() {

    function Node(value) {
        this.value = value;
        this.left = null;
        this.right = null;
    }

    this.root = null;

    this.addNode = function(value) {
        let node = new Node(value);
        if (!this.root) {
            this.root = node;
        } else {
            insertNode(this.root, node);
        }
    }

    function insertNode(currentNode, newNode) {
        if (newNode.value < currentNode.value) {
            if (!currentNode.left) {
                currentNode.left = newNode;
            } else {
                insertNode(currentNode.left, newNode);
            }
        } else {
            if (!currentNode.right) {
                currentNode.right = newNode;
            } else {
                insertNode(currentNode.right, newNode);
            }
        }
    }

    this.postOrderTraversal = function(callback) {
        postOrderTraversalHelper(this.root, callback);
    }

    function postOrderTraversalHelper(node, callback) {
        if (node) {
            callback(node.value);
            postOrderTraversalHelper(node.left, callback);
            postOrderTraversalHelper(node.right, callback);
        }
    }

}

let tree = new BinarySearchTree();
tree.addNode(3);
tree.addNode(5);
tree.addNode(14);
tree.addNode(11);
tree.addNode(25);
tree.addNode(2);

tree.postOrderTraversal(function log(value) {
    console.log(value);
});