Count number of returned rows for menu items

i have 2 tables: Categories,Oglasi

categories
category_id | category | parent
1             auto      0
2             games     0
3             bmw       1
4             cards     2

oglasi
oglas_id | category_id
1          3            
2          4             

What im trying to do is make a menu of this as:

parent name - category name ( number of items in this category)

Example : auto - bmw ( 1 )

Now i got it to make a tree menu of parent name-category name,but don't know how to connect all of this with the counted rows number. Here's my query and code to do this:

$kategorije = dbQuerySelect('SELECT a.category parent
                                  , b.category child
                                  FROM categories a
                                  JOIN categories b
                                  ON a.category_id = b.parent
                                  ORDER BY a.category_id');
                if ($kategorije)
                  {
                    $parent = '';
                    echo "<ul>";
                    foreach ($kategorije as $next) {
                       if ($next['parent'] != $parent) {
                          if (strlen($parent) > 0) {
                             echo "    </ul>";
                             echo "  </li>";
                          }
                          echo "  <li>" . $next['parent'];
                          echo "    <ul>";
                       }
                       echo "    <li>" . $next['child'] . "</li>";

                       $parent = $next['parent'];
                    }
                    echo "    </ul>";
                    echo "  </li>";
                    echo "</ul>";
                  }

So in this case this returns:

parent | child
auto     bmw
games    cards

Can someone please help me to edit my code and return the number of rows in each 'subcategory' ? I tried a fe开发者_JAVA技巧w variations with COUNT in the query,but i just couldn't make it work.

SELECT a.category parent, 
       b.category child,
       (select count(*) from oglasi where category_id = b.category_id) as count
FROM categories a
JOIN categories b
ON a.category_id = b.parent
ORDER BY a.category_id

With this you should get:

   parent|child|count
   auto  bmw    1