src/Page/Product.php
private function getCategoryOptionsNoParent()
    {
        $ancestors = $this->getAncestors()->column('ID');
        $categories = ProductCategory::get();
        if (!empty($ancestors)) {
            $categories = $categories->exclude('ID', $ancestors);
        }
        return $categories->map('ID', 'NestedTitle')->toArray();
    }
private function getCategoryOptionsNoParent()
    {
        $ancestors = $this->getAncestors()->column('ID');
        $categories = ProductCategory::get();
        if (!empty($ancestors)) {
            $categories = $categories->exclude('ID', $ancestors);
        }
        return $categories->map('ID', 'NestedTitle')->toArray();
    }
Helper function for generating a list of additional categories excluding the main parent.

@return array categories