src/Page/ProductCategory.php
public function GroupsMenu()
    {
        if ($this->Parent() instanceof ProductCategory) {
            return $this->Parent()->GroupsMenu();
        }
        return ProductCategory::get()
            ->filter('ParentID', $this->ID);
    }
public function GroupsMenu()
    {
        if ($this->Parent() instanceof ProductCategory) {
            return $this->Parent()->GroupsMenu();
        }
        return ProductCategory::get()
            ->filter('ParentID', $this->ID);
    }
Recursively generate a product menu, starting from the topmost category.

@return DataList