Merchants can enable a dropdown filter to appear on the Bundle page.
This will create a down-down filter, with a range of filter options based of tags, attached to your products.
Inside the Bundle configuration, an option to enable the product filters is set below the description.
Enable this checkbox to display a dropdown on your bundle page.
Tags can be added to products through the Shopify dashboard - Navigating to Products, selecting the individual Products you've selected for inclusion in a given bundle and applying a tag via the sub-menu, illustrated below.