使用php mysql进行更深入的子类别

I have a problem with creating multiple sub category with php and mysql where the deeper sub category doesn't get indented. The screenshot is just like:
.
The sealer and wall paint should be indented like hobe.

Ex: 1. painting, 1.1 HOBE, 1.1.1 Sealer, 1.1.2 Wall Paint

I have 3 table:

1. kategori contain: id_kat, nama_kat

2. subkategori contain: id_subkat, id_kat, nama_subkat

3. supersubkategori contain: id_supersub, id_subkat, id_kat, nama_supersub

My code is:

include "config.php";
$sql = mysql_query("SELECT * FROM kategori");
while($data=mysql_fetch_array($sql)) 
{
    echo "<li>".$data['nama_kat'].""; // kategori

    $sql2 = mysql_query("SELECT * FROM subkategori WHERE id_kat = '".$data['id_kat']."'"); // sub kategori
    if($sql2) 
    {
        echo "<ul>";
            while($data2=mysql_fetch_array($sql2)) 
            {
                echo "<li>".$data2['nama_sub']."</li>";
            }
        echo "</ul>";
    }
    echo "<li>";
        $sql3 = mysql_query("SELECT * FROM supersubkategori WHERE id_kat = '".$data['id_kat']."'"); // supersub kategori
        if($sql3) 
        {
            echo "<ul>";
                while($data3=mysql_fetch_array($sql3)) 
                {
                    echo "<li><a href='cat.php?kategori=$data3[nama_supersub]'>".$data3['nama_supersub']."</a></li>";
                }
            echo "</ul>";
        }

    else 
    {
        echo "</li>";
    }

}
?>

I really thankful if someone can help me how solve this problem. Thank you