void removeDuplicates() {
        Node current = this;
        while(current != null) {
            Node runner = current;
            while(runner.next != null) {
                if(runner.next.data == current.data) {
                    runner.next = runner.next.next;
                }
                else {
                    runner = runner.next;
                }
            }
            current = current.next;
        }
    }