This article explains how to migrate Confluence plugins from one Cloud instance to another.
Introduction
For Copy Page Tree you don't need to take any extra steps. The Copy Page Tree plugin does not store any of your content. It is briefly touched during the copy process, but once that has been completed, the plugin has nothing more to do with it. If you would like to continue using the plugin in the new instance, you will need a license there.
Prerequisites
You must have a license for the plugin you want to migrate.
You must have access to the source and target Confluence Cloud instances.
Steps
On the source Cloud instance, install the Copy Page Tree plugin.
Export the content of the Confluence space that contains the plugin.
Import the content of the Confluence space into the target Cloud instance.