graph g {
    node [ shape="circle" ];
    {
        rank="same";
        1;
        2;
        5;
        6;
    }

    {
        rank="same";
        3;
        4;
        7;
    }

    1 -- 2;
    1 -- 3;
    1 -- 4;
    2 -- 4;
    5 -- 7;
}