With PediTree, it is possible to have two (or more) copies running at the same time, each showing a different database. This wasn't anticipated initially, but several users have found it to work without issues. So here is some information about this.
There are several ways to set up multiple copies of PediTree for this purpose. Some work well, others are a bit clumsy. Working in Windows 10, here is one setup that seems easy to use.