The Trees sidebar command opens a screen that lets you modify the Trees for the current Person or Family. It also lets you Include relatives. Due to a dubious family entered by someone else, when I used the Include relatives on one of my Trees I unexpectedly acquired over a thousand suspect Wilson "ancestors".
There is no obvious way to prune the Tree except to either delete it and start over or to search out and remove all of the unwanted "ancestors".
It would be helpful when using the Include relatives feature to add a dialog stating the results and then allowing to accept or reject. However this would be problematic as the Include relatives function wisely runs in the background and the results might not be available for some time.
Alternatively I would like to see a Remove relatives feature added to the Trees screen that can be used in the same way as the Include relatives now works.