Building a treeview

Question

I'm trying to build an treeview but im totally stuck.

Here's my table id int(11),
naam varchar(255),
parent int(11),
active int(11)

Here the is the code (the data comes trough the class ContentCategory)

$ContentCategories = ContentCategory::getContentCategories();

<ul>
                            <?php 
                            foreach ($ContentCategories as $ContentCategory) {
                                if ($ContentCategory->parent == 0){
                                    ?>
                                    <li><?php echo $ContentCategory->naam?></li>    
                                    <?php                                                       
                                    $parent_id = $ContentCategory->id; 
                                }
                                if ($ContentCategory->id = $parent_id && $ContentCategory->parent !=0) {
                                    echo "------".$ContentCategory->naam.'<br />';
                                    $sparent_id = $ContentCategory->parent;
                                }                               
                                echo $sparent_id;
                                print_pre($ContentCategory);
                            }   
                            ?>
                        </ul>

This gives me the headcategories and the categories who are below it, now i'd like to get the next branches, it needs to be possible te make as many branches as i like.

But the problem is that i don't have a clue how to fix this.