Theme with special feature for subpage

Hello,

First of all I would like to thank the people who works so hard to develop wordpress. I just started using it.

I am looking for a theme, that will show the main pages in the sidebar, and only those subpages that are under the current page. The subpages that are under other pages will not be visible in the current page. I wasn’t sure how to search this topic, so I am just posting it. If any previous posts were made regarding this topic I am truly sorry. Please help me out. Thank you