This is the background. After entering the background, click "Custom Menu Bar" on the left, and click "+"on the right of "Menu Management" to display the first-level menu. After setting the first-level menu, it will appear below the menu management, and then click the "+"sign on the right side of the first-level menu you set to set the second-level menu. Up to five second-level menus can be set.

You cannot set a submenu below the second level.