Create buy one get one free or buy X get Y of product free discount rule in your WooCommerce based website
Buy One Get One Nulled (or BOGO for short) is one of the best offers you can use to clear out and move inventory and generate more cash. People have to buy more to get the offer, so you get more money.
Demo : https://woocommerce.com/products/buy-one-get-one-free/