This is not an out-of-the box/core function you can easily configure from the settings.
You need to modify shop pages' loop function.
Or there is a third party extension listed in the http://www.woothemes.com/product-category/woocommerce-extensions/ page:
WooCommerce Nested Category Layout
http://www.foxrunsoftware.net/shop/wordpress-plugins/woocommerce-nested-category-layout/