Recursive function for a TYPO3 sys_category tree

$categories = $this->categoryRepository->findAll()->toArray();
$categoriesTree = $this->buildTree($categories);
$this->view->assign('categories', $categoriesTree);

public function buildTree($elements, $parentId = null)
{
    $tree = array();
    
    foreach ($elements as $element) {
        if ($element->getParent() == $parentId) {

            $children = $this->categoryRepository->findByParent($element->getUid());

            if ($children) {
                $this->buildTree($elements, $element->getUid());
                $element->setChildren($children);
            }

            $tree[] = $element;
        }
    }

    return $tree;
}

<f:render partial="Field/CategoriesTree" arguments="{categories:categories}"/>

Field/CategoriesTree.html

<ul>
    <f:for as="category" each="{categories}">
        <li>
            {category.title}

            <f:if condition="{category.children}">

                    <f:render partial="Field/CategoriesTree" arguments="{categories:category.children}"/>

            </f:if>
        </li>
    </f:for>
</ul>