You don't install the license directly on a VM ISE node, but on the admin node of the deployment. It is a 1 for 1 utilization where you need a VM node license to cover each VM node in the deployment.
When you fulfill the VM licenses, you do so entering the primary and secondary admin UDI details. If you have 10 licenses, then those 10 are pooled and available for use when you add nodes.
The alternative is to use smart licensing, you can add all your licenses to your smart virtual account and ISE will leverage them from there.
Regardless if how you go about doing it, smart or traditional, you need 1 VM license per VM node you deploy.