module ActiveAdmin::Menu::MenuNode

If this ID is already taken, transfer the children of the existing item to the new item.
The method that actually adds new menu items. Called by the public method.

def _add(options)
  item = ActiveAdmin::MenuItem.new(options)
  item.send :children=, self[item.id].children if self[item.id]
  self[item.id] = item
end