Greg Popov

public static function getTree($categories, $left = 0, $right = null, $lvl = 1){

        $tree = [];

        foreach ($categories as $index => $category) {
            if ($category->lft >= $left + 1 && (is_null($right) || $category->rgt <= $right) && $category->lvl == $lvl) {
                $tree[$index] = [
                    'id' => $category->id,
                    'label' => $category->name,
                    'url' => ['/shop/catalog/list', 'id' => $category->id],
                    'items' => self::getTree($categories, $category->lft, $category->rgt, $category->lvl + 1),
                ];
            }
        }

        return $tree;

    }
    
    public static function getFullTreeStructure(){

        $roots = Category::find()->roots()->addOrderBy('root, lft')->all();
        $tree = [];
        foreach ($roots as $root){
            $tree [] = [
                'id' => $root->id,
                'label' => $root->name,
                'url' => ['/shop/catalog/list', 'id' => $root->id],
                'items' => self::getTree($root->children()->all()),
            ];
        }

        return $tree;
    }