Hi CTAiLLC​ Clicking Add to Calendar downloads an .ics file. Outlook supports this file type.

Go to Outlook and open your calendar, then right click the iCalendar file to open with Outlook, you'll see the Add calendar > Upload from file window pop up. (Note: this window won't appear if you are in Outlook email; you must navigate to calendar view.) Choose the calendar to add the event to and select "Import".