graph k4 {
    splines=false;
    node [ shape="point" ];
    {
        rank="same";
        3;
        5;
        4;
    }
    1 -- 6 -- 2;
    1 -- 3;
    1 -- 4;
    2 -- 3;
    2 -- 4;
    3 -- 5;
    5 -- 4;
}