Loop through menu items recursively starting from second level - php

Question

I have navigation which looks like this in the system:
At the moment, I am able to print an array of objects containing the menu items recursively, and the code looks like this:
public function get() {
$current_path = \Drupal::service('path.current')->getPath();
$path_items = explode ('/',$current_path);
$menu_array = [];
$menu = $path_items[4];
if(!empty ($menu) ){
$sub_nav = \Drupal::menuTree()->load($menu, new \Drupal\Core\Menu\MenuTreeParameters());
foreach($sub_nav as $nav){
array_push($menu_array, $nav);
}
$manipulators = array(
array('callable' => 'menu.default_tree_manipulators:generateIndexAndSort'),
);
$sub_nav = \Drupal::menuTree()->transform($sub_nav, $manipulators);
$this->generateSubMenuTree($menu_array, $sub_nav);
$response = array_values($menu_array);
}
return (new ResourceResponse($response))->addCacheableDependency(array('#cache' => array('max-age' => 0)));
}
private function generateSubMenuTree(&$output, &$input, $parent = FALSE) {
$input = array_values($input);
$items = 0;
foreach($input as $key => $item) {
//If menu element disabled skip this branch
if ($item->link->isEnabled()) {
if ($item->link instanceof \Drupal\menu_link_content\Plugin\Menu\MenuLinkContent) {
$uuid = $item->link->getDerivativeId();
$entity = \Drupal::service('entity.repository')
->loadEntityByUuid('menu_link_content', $uuid);
}
$link_data['name'] = $item->link->getTitle();
if(!empty($item->link->pluginDefinition['url'])){
$link_data['href'] = $item->link->pluginDefinition['url'];
}
//If not root element, add as child
if ($parent === FALSE) {
$output[$key] = $link_data;
} else {
$output['children'][$key] = $link_data;
}
if ($item->hasChildren) {
if ($item->depth == 1) {
$this->generateSubMenuTree($output[$key], $item->subtree, $key);
} else {
$this->generateSubMenuTree($output['children'][$key], $item->subtree, $key);
}
}
$items ++;
}
}
}
The code above results into the following:
However my specification now changed in the sense that for Nav Data and Departments, I should only start including from the child elements onwards.
The result should be something like this:
{
[
{
name : "Shop"
children : [
{
name : "Promotions"
tabletColumn : 0
desktopColumn : 0
children : [...] 3 items
},
{ ... }
]
},
{...}
],
[
{
name : "Personal"
children : [...] 0 items
selected : true
}
],
{...}
{...}
}
Have been struggling with this logic for 24 hours already.