WP menu custom container

functions.php

//
// Custom WP menu container - thanks to https://gist.github.com/nikolov-tmw/8698598
//
// Add a custom container to your 
//
add_action( 'admin_head-nav-menus.php', 'custom_register_menu_metabox' );

function custom_register_menu_metabox() {
	$custom_param = array( 0 => 'mega_col' );
	
	add_meta_box( 'custom-nav-container-metabox', 'Custom Nav Container', 'custom_nav_container_metabox', 'nav-menus', 'side', 'default', $custom_param );
}

function custom_nav_container_metabox( $object, $args ) {
	global $nav_menu_selected_id;

	// Create an array of objects that imitate Post objects
	$my_items = array(
		(object) array(
			'ID' => 1,
			'db_id' => 0,
			'menu_item_parent' => 0,
			'object_id' => 1,
			'post_parent' => 0,
			'type' => 'custom_nav_container',
			'object' => 'custom-nav-container',
			'type_label' => 'Custom Nav Container',
			'title' => 'Custom Nav Container',
			'url' => home_url( '#' ),
			'target' => '',
			'attr_title' => '',
			'description' => '',
			'classes' => array(),
			'xfn' => '',
		),

	);
	$db_fields = false;
	// If your links will be hieararchical, adjust the $db_fields array below
	if ( false ) {
		$db_fields = array( 'parent' => 'parent', 'id' => 'post_parent' );
	}
	$walker = new Walker_Nav_Menu_Checklist( $db_fields );

	$removed_args = array(
		'action',
		'customlink-tab',
		'edit-menu-item',
		'menu-item',
		'page-tab',
		'_wpnonce',
	); ?>
	<div id="custom-container-div">
		<div id="tabs-panel-custom-container-all" class="tabs-panel tabs-panel-active">
		<ul id="custom-container-checklist-pop" class="categorychecklist form-no-clear" >
			<?php echo walk_nav_menu_tree( array_map( 'wp_setup_nav_menu_item', $my_items ), 0, (object) array( 'walker' => $walker ) ); ?>
		</ul>

		<p class="button-controls">
			<span class="list-controls">
				<a href="<?php
					echo esc_url(add_query_arg(
						array(
							'custom-container-all' => 'all',
							'selectall' => 1,
						),
						remove_query_arg( $removed_args )
					));
				?>#my-menu-test-metabox" class="select-all"><?php _e( 'Select All' ); ?></a>
			</span>
			<span class="add-to-menu">
				<input type="submit"<?php wp_nav_menu_disabled_check( $nav_menu_selected_id ); ?> class="button-secondary submit-add-to-menu right" value="<?php esc_attr_e( 'Add to Menu' ); ?>" name="add-custom-container-menu-item" id="submit-custom-container-div" />
				<span class="spinner"></span>
			</span>
		</p>
	</div>
	<?php
}