Drop-down submenu (in a vertical menu)

Currently, there are two options for expanding submenus in a vertical menu: left and right. For menus with more subpages (two- or three-level menus), it would be great to have the option to expand submenus downward so they remain visible at all times—which would be useful, for example, in an online store where product categories are organized under parent categories. Thank you for your work :)