The menu editor works for the most part as the dialog editor. A single left click on a menu title will fold down the menu items.
If a menu title is copied, deleted or moved, then also the corresponding entries are copied, deleted or moved.
It should be noted that the menu editor for any modification of an entry usually always recalculates the entire menu, and sets all entries of a sub-menu to the same width, and realigns any shortcuts. Of course this functionality only works if it is a "normal" menu which is composed of only vertically aligned strings.