espensl

Here is the code that sets up the CPT and adds the “parent_id” field meta box.

function create_post_type(){
	$labels = array(
		'name' => _x('Creditors','post type general name'),
		'singular_name' => _x('Creditor', 'post type singular name'),
		'add_new' => _x('Add New', 'creditor'),
		'add_new_item' => __('Add New Creditor'),
		'edit_item' => __('Edit Creditor'),
		'new_item' => __('New Creditor'),
		'all_items' => __('All Creditors'),
		'view_item' => __('View Creditor'),
		'menu_name' => __('Creditors'),
		'parent_item_colon' => ''
	);
	$args = array(
		'public' => true,
		'hierarchical' => true,
		'labels' => $labels,
		'rewrite' => array('slug' => 'tilbydere'),
		'has_archive' => true
		);
	register_post_type('creditor', $args);
}

function creditor_custom_parent_setup(){
	global $post;
	$post_type_object = get_post_type_object($post->post_type);
	if ( $post_type_object->hierarchical ) {
	  $pages = wp_dropdown_pages(array(
      								'post_type' =>  'page',
      								'selected' => $post->post_parent,
      								'name' => 'parent_id',
      								'show_option_none' => __('(no parent)'),
      								'sort_column'=> 'menu_order, post_title',
      								'echo' => 0)
								);
      if ( !empty($pages) ) {
        echo $pages;
        echo '<input type="hidden" name="parent_id_noncename" value="' . wp_create_nonce(__FILE__) . '" />';
      } // end empty pages check
	}
}