graph g {
    node [ shape="point" ];
    {
        rank="same";
        1 [ xlabel="1" ];
        2 [ xlabel="2" ];
    }
    {
        rank="same";
        3 [ xlabel="3" ];
        4 [ xlabel="4" ];
    }
    1 -- 2;
    1 -- 3;
    1 -- 4;
    3 -- 4;
}