RSS Feed show sub category items in top cat

Hi how can i make rss feed show items from the last sub category in top category?


all my items a in the last category

computer/consumer/lenovo/i5 items here

i want to show items here

computer and consumer and lenovo and i5

so a customer can use the rss feed from lats say consumer to get all updates from aall sub categorys from consumer and down

any idea on how to achieve this?