WordPress: Using same template to categories and child categ

function load_tax_parent_template() {
    global $wp_query;

    if (!$wp_query->is_tax)
        return true; // saves a bit of nesting

    // get current category object
    $tax = $wp_query->get_queried_object();

    // trace back the parent hierarchy and locate a template
    while ($tax && !is_wp_error($tax)) {
        $template = STYLESHEETPATH . "/taxonomy-{$tax->slug}.php";

        if (file_exists($template)) {
            load_template($template);
            exit;
        }

        $tax = $tax->parent ? get_term($tax->parent, $tax->taxonomy) : false;
    }
}
add_action('template_redirect', 'load_tax_parent_template');