notes/school/di-ma/20181106_2-tree.dot

graph g {
    node [ shape="circle" ];
    {
        rank="same";
        2;
        3;
    }
    {
        rank="same";
        5;
        6;
    }

    1 -- 2;
    1 -- 3;
    3 -- 4;
    4 -- 5;
    4 -- 6;
}