mathieuhays

This plugin allows you to duplicate a menu item, sub-items included in Appearance > Menus.

Menu Item Duplicator

Good plugin, does the job perfectly.

There is no help file, but the duplicate button is at the bottom of the menu item where it would be expected and it duplicates all the menu items below the parent. This is all the help information that you need.

This plugin saved me a lot of time when I needed to duplicate the items in a menu.

Nice Plugin

Allow you to duplicate menu items and their sub-elements in Appearance > Menus

caterhamcomputing

CC Duplicate Menu adds a Duplicate Menu button to the WordPress menu editor, allowing you to create a full copy of an existing navigation menu.
The duplicated menu:
<ul>
<li>uses the original menu name with “ (copy)” appended</li>
<li>keeps the same links and labels</li>
<li>preserves menu hierarchy and order</li>
<li>creates new menu items so the copied menu can be edited independently</li>
</ul>
The plugin is built with security, privacy and WordPress coding standards in mind.

CC Duplicate Menu

Safely duplicate WordPress navigation menus from the menu editor.

Menu Item Duplicator vs CC Duplicate Menu