There probably is, and an Internet search should reveal it. A simple but
slow way is to copy the smaller parent folder onto the larger, telling it to
autoskip duplicates when they occur. Then you should wind up with the same
number of files and folders in each. If not, because there are some files
and/or folders that are still not common to both, just copy the other
direction. Barring a bad copy operation (very rare) you then have what you
wanted.