This is a frequently asked for feature, that we have deliberately not implemented yet. It’s not hard technically, but it has historically caused some major problems for users not realizing the full consequences (i.e. Encrypt c:\ recursive – yay, let’s encrypt everything, that must be secure!).
We’ve had product planning meetings and discussions about how to ensure simple operation for most users, without exposing lots of options, while still enabling such functionality for users who are qualified to use them properly. We’re getting to a point where we have a concept we think will work, so it’s now on the list.