digraph subject {
    size="6,6";
    node [color=lightblue2, style=filled];
    rankdir=LR;
    
    
    s10[label="k=0"];
    s11[label="k=1"];
    s1other[label="...", style=none, border=0, color=white];

    s20[label="k=0"];
    s21[label="k=1"];
    s2other[label="...", style=none, border=0, color=white];

    F1[label="subject #1"];
    F2[label="subject #2"];
    
    
    ""->F1;
    ""->F2;
    F1->s10;
    F1->s11;
    F1->s1other;

    F2->s20;
    F2->s21;
    F2->s2other;
    
}