CPT parent example

// In functions.php

/**
 * Custom Post Type
 */
class location_post_type {

    function location_post_type() {
        add_action('init',array($this,'create_post_type'));
    }

    function create_post_type() {
        $labels = array(
            'name' => 'Locations',
            'singular_name' => 'Location',
            'add_new' => 'Add New',
            'all_items' => 'All Locations',
            'add_new_item' => 'Add New Location',
            'edit_item' => 'Edit Location',
            'new_item' => 'New Location',
            'view_item' => 'View Location',
            'search_items' => 'Search Locations',
            'not_found' =>  'No Locations found',
            'not_found_in_trash' => 'No Locations found in trash',
            'parent_item_colon' => 'Parent Location:',
            'menu_name' => 'Locations'
        );
        $args = array(
            'labels' => $labels,
            'description' => "A description for your Location type",
            'public' => true,
            'exclude_from_search' => true,
            'publicly_queryable' => true,
            'show_ui' => true,
            'show_in_nav_menus' => true,
            'show_in_menu' => true,
            'show_in_admin_bar' => true,
            'menu_position' => 20,
            'menu_icon' => '/absolute/url/to/icon',
            'capability_type' => 'post',
            'hierarchical' => true,
            'supports' => array('title','editor','page-attributes'),
            'has_archive' => true,
            'rewrite' => array('slug' => 'your-slug', 'with_front' => 'before-your-slug'),
            'query_var' => true,
            'can_export' => true
        );
        register_post_type('location_post_type',$args);
    }
}

$location_post_type = new location_post_type();


/**
 * Add Parent dropdown to 'pages' that lists all location CPTs
 */
add_action('admin_menu', function() { remove_meta_box('pageparentdiv', 'location_post_type', 'normal');});
add_action('add_meta_boxes', function() { add_meta_box('page-parent', 'Parent', 'my_page_attributes_meta_box', 'page', 'side', 'high');});

function my_page_attributes_meta_box($post) {
    $post_type_object = get_post_type_object($post->post_type);
    if ( $post_type_object->hierarchical ) {
      $pages = wp_dropdown_pages(array('post_type' => 'location_post_type', '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;
      } // end empty pages check
    } // end hierarchical check.
  }