The TreeRefiner Add-in Part provides a search refiner for your search center that displays a tree of terms that are contained in the search results. It complements the SharePoint-refiners and can be added into the search center.
This SharePoint add-in works in conjunction with another add-in, which is only available from DIQA and which requires installation on your environment outside of the Microsoft Office Store processes due the level of required permissions. A tenant administrator will need to deploy this specific add-in to the tenant manually, so that it can be installed to your environment. When apps are installed outside of the Microsoft Office Store, they may bypass any, and all, safety and security checks provided by Microsoft. Consider trying this add-in on a separate SharePoint Tenancy before installing it on your primary SharePoint site(s)
How to download and install this additional add-in is explained in the installation guide provided with the TreeRefiner Add-in.