WordPress sub-menu items split in 2 columns

Let’s say you have a long list of items in one of your WordPress sub-menu drop downs. It is often the case with Products or Services sections of the site. So, you probably want those sub-menu items to be split in 2 columns. But you want 2 columns only in certain sub-menus, and you don’t want to overly complicate things with a mega-menu WP plugin. Well, there is an easy way to achieve this using flexibility and power of WP menus, and CSS :nth-child() selector.