wp_list_pages grandchild brakes order

Hello

I have product navigation menu from pages like

• Cat 1

• Product 1
• Product 2

• Model 1
• Model 2

• Cat 2
• Cat 3

When I click on Model 1, my menu collapses and become

• Cat 1
• Cat 2
• Cat 3
• Model 1
• Model 2

How can I change this, so the menu stays expandend on Model 1 or Model 2

I’am using code from here

$ancestor_id = 1843; // you want to change this
$descendants = get_pages( array( 'child_of' => $ancestor_id ) );
$incl = '';

foreach ( $descendants as $page ) {
    if ( ( $page->post_parent == $ancestor_id )
        || ( $page->post_parent == $post->post_parent )
        || ( $page->post_parent == $post->ID )
    ) {
        $incl .= $page->ID . ",";
    }
}
?>

<ul>
    <?php
    wp_list_pages( array(
        'child_of'    => $ancestor_id,
        'include'     => $incl,
        'link_before' => '',
        'title_li'    => '',
        'sort_column' => 'menu_order'
    ) );
    ?>
</ul>