PHP - Parallel Foreach Loops

I'm trying to build a tree to display product groups, but I can't achieve what I want.

There is a hierarchy for the tree which I need to follow:

1H
  1HS
    1HSMP

I want to list all the categories (1H) with its subcategories(1HS), and it's subcategories (1HSMP).

This is the code I'm currently using:

<ul>
                                                            <?php
                                                            //Here we fetch category
                                                            $categories_list = array();
                                                            if($stmt = $conn -> prepare("SELECT a.category, a.subcategory, a.subcategory1, a.category_description, a.subcategory_description, a.subcategory_description1,  SUM(nsq.sales_amount) AS sales, SUM(nsq.sales_amount+nsq.cost_amount) AS RUC
                                                                                                FROM dpb.articles a
                                                                                                LEFT JOIN dpb.nav_sales_qty nsq
                                                                                                ON nsq.article_no = a.article_no
                                                                                                WHERE nsq.entry_type_desc = 'Prodaja'
                                                                                                GROUP BY a.subcategory1")) {
                                                               $stmt -> execute();
                                                               $stmt -> store_result();
                                                               $stmt -> bind_result($category, $subcategory, $subcategory1, $category_description, $subcategory_description, $subcategory_description1, $total_sales, $total_profit);
                                                               while($stmt -> fetch()) {
                                                                   $categories_list[] = array('category' => $category,
                                                                                               'subcategory' => $subcategory,
                                                                                               'subcategory1' => $subcategory1,
                                                                                               'category_description' => $category_description,
                                                                                               'subcategory_description' => $subcategory_description,
                                                                                               'subcategory_description1' => $subcategory_description1,
                                                                                               'total_profit' => $total_profit,
                                                                                               'total_sales' => $total_sales);
                                                               }
                                                               $stmt -> close();
                                                            }

                                                            foreach($categories_list as $key => $value) {
                                                            ?>
                                                                <li><?php echo $value['category'].' - '.$value['category_description']; ?>
                                                                    <ul>
                                                                        <?php
                                                                        //Here we filter subcategory
                                                                        if(strpos($value['subcategory'], $value['category']) === 0) {
                                                                            //Iterate over subcategory
                                                                            foreach ($value as $key2 => $value2) {
                                                                                debugVar($value2);
                                                                        ?>

                                                                                <li data-jstree='{"opened":true}'><?php echo $value2['subcategory'] . ' - ' . $value2['subcategory_description']; ?>
                                                                                    <ul>

                                                                                        <?php
                                                                                        //Here we filter subcategory2
                                                                                        if (strpos($value['subcategory1'], $value['subcategory']) !== false) {
                                                                                            ?>

                                                                                            <li data-jstree='{"type":"file"}'>
                                                                                                <?php echo $value['subcategory1']; ?>
                                                                                            </li>

                                                                                            <?php
                                                                                            //Here we close subcategory1 if statement
                                                                                        }
                                                                                        ?>

                                                                                    </ul>
                                                                                </li>
                                                                                <?php
                                                                                //Here we close subcategory if statement
                                                                            }
                                                                        }
                                                                        ?>
                                                                    </ul>
                                                                </li>

                                                            <?php
                                                            //Close foreach loop
                                                            }
                                                            ?>
                                                            </ul>

  The result I'm getting is attached in the photo, and it's not what I want!

The result I need is the following:

I find a category (1H), and then I find all of its subcategories which are 1H% (all that start with 1H) and display them bellow 1H. Then I iterate over all of these subcategories (example 1HS%, 1HP%, 1HRD%) and I find all of their subcategories which are starting with (1HS, 1HP, 1HRD) and display them.

Example:

1H
  1HS
    1HSMP
    1HSTR
    1HSKT
  1HP
    1HPSD
    1HPDD
    1HPSA
  1HRD
    1HRDA
    1HRDBV
   1HRDTE
   1HRDEF

Can you please help me how to achieve that? I spent a lot of time, and I can't get the proper result.

In order to solve my problem I have been told to use multi threading, In my research I have found parallel because thread is not recommended for web server environments, What is CLI? 

php.net has the info but I may just be a little stupid, When looking for more information, I found something called compose, which I may need to install, but I am using shared hosting so it may not be possible. I have found that many hosts are unwilling to do anything beyond the basics. 

1. Can parallel be used without installing these added dependencies or packages? 
2. Is there a simple to understand explanation somewhere of this? I have Googled but am just getting more and more confused.