You can create an easy-to-use accordion dropdown for your categories with this plugin from YITH. This widget can replace the category list widget that comes with your site.
With this plugin, you can choose which categories to display and they will look better. A maximum number of categories can be set, empty categories can be hidden, and subcategories can be shown or hidden.
You shouldn’t use this plugin if you want to remove all traces of a category from your site. Instead, you can use this plugin to replace the widget that lists your product categories so you can leave out categories and subcategories that don’t have any products.