Permissions problem - setting up dirs for root + group access
I have a source tree owned by root (a website). I created a new group called deploy and added a user to it also called deploy. What I want is both the groups [root] and [deploy] to have write access to the full tree, i.e. from www downwards. This is so the deploy user can update the source via FTP when needed, but it still secure because its owned by root and "deploy" can only update this tree. How is this done please? Thanks...