sub tree {
    ($h,$f,$s)=@_;
    split//,'0@*+'x(10*$f).'='x(40*(1-$f));
    for(0..$h-1){
        $s.=$/.$"x($h-$_);
        $s.=$_[rand@_]for+0..2*$_
    }
    $s=~s/\S/*/;
    print$s
}