// Just change your the TreeNode references to your class
public void print()
    {
        TreeNode<E> currentNode = tree;
        printNode(tree);
    }
    private void printNode(TreeNode<E> node)
    {
        if (node != null)
        {
            System.out.print(node.value + " ,");
            if (node.left != null)
            {
                printNode(node.left);
            }
            if (node.right != null)
            {
                printNode(node.right);
            }
        }
    }