branch specification based on parent

I am using Team City with Stash.

When I create a new branch it's either a feature or a bugfix that will branch from either master or X, what I would like to do is say that I will only build that if it's parent branch is X, but I am not sure how do do that in the branch specification.  Can one of you wizards point me in the right direction?

Is it something along the lines of:

+: feature* ^X
+: bugfix* ^X


thanks!