[fluid collapsible table with php?]

I'm perty sure this can be done, I just don't know how. I want to change this category map (not Menu) to be fluid and collapsible. This is my current code:
[code]$c = $this->Categories;

$categorymap = '';
$count = 0;
for ($i=0; $i<sizeof($c); $i++){

  if ($c[$i]->parentid == 0){
    $count++;
    if ($count == 1){
        $categorymap .= '<tr>';
    }
    $categorymap .= '<td valign=top>'."<a style='font-size:110%' href='{$c[$i]->url}'>{$c[$i]->title}</a>".'<br>';
    for ($k=0; $k<sizeof($c); $k++){
        if ($c[$k]->parentid == $c[$i]->id){  //subcategory
          $categorymap .= " &nbsp; <a href='{$c[$k]->url}'>{$c[$k]->title}</a>" .'<br>';
        }
    }
    $categorymap .= '</td>';
    if ($count == 3){
        $categorymap .= '</tr>';
        $count = 0;
    }
  }
}
if ($count != 0){
  $categorymap .= '</tr>';
}
[/code]

What do I need to change to get this to look even and be collapsible?

I Apreciate the help!