class UndirectedTree {

    public void addRelationship(int node1, int node2) {
        if (node1 < node2) {
            addChild(node1, node2);
        } else if (node1 > node2) {
            addChild(node2, node1);
        }
        // do nothing on node1 == node2
    }

    public  UndirectedTree(int capacity);

}