wp how to call parent category template

1// Use a parent category slug if it exists
2function child_force_category_template($template) {
3    $cat = get_query_var('cat');
4    $category = get_category($cat);
5
6    if ( file_exists(TEMPLATEPATH . '/category-' . $category->cat_ID . '.php') ) {
7        $cat_template = TEMPLATEPATH . '/category-' . $category ->cat_ID . '.php';
8    } elseif ( file_exists(TEMPLATEPATH . '/category-' . $category->slug . '.php') ) {
9        $cat_template = TEMPLATEPATH . '/category-' . $category ->slug . '.php';
10    } elseif ( file_exists(TEMPLATEPATH . '/category-' . $category->category_parent . '.php') ) {
11        $cat_template = TEMPLATEPATH . '/category-' . $category->category_parent . '.php';
12    } else {
13        // Get Parent Slug
14        $cat_parent = get_category($category->category_parent);
15
16        if ( file_exists(TEMPLATEPATH . '/category-' . $cat_parent->slug . '.php') ) {
17            $cat_template = TEMPLATEPATH . '/category-' . $cat_parent->slug . '.php';
18        } else {
19            $cat_template = $template;
20        }
21
22    }
23
24    return $cat_template;
25}
26add_action('category_template', 'child_force_category_template');
27