Dirdiff can handle up to 5 trees. It displays a main window with a list of the files which are different between the trees, with colored squares to indicate the relative ages of the versions. A menu allows you to display the differences between any two of the versions in another window. Another menu allows you to copy the file from one tree to another.
Needs to be launched from the command line, and hasn't been updated for years... But it still works and is the best GUI tool I have found so far for comparing similar folder structures like originals with backups.