foreach ($folders as $key=>$value){
    echo "$key - $value<br>";
    if(is_array($value)&&count($value)>0) {
        foreach ($value as $tmp=>$key2){
            echo "$tmp - $key2<br>";
            if(is_array($key2)&&count($key2)>0){
                foreach ($key2 as $tmp2=>$key3){
                    echo "$tmp2 - $key3 <br>";
                }
            }
        }
    }
}