Please copy this link and follow the instructions below.
webcal://www.nischina.org/cf_calendar/feed.cfm?type=ical&feedID=816EF81278F5421085C1B30E9B336F5E
Navigate to https://outlook.office.com/mail/
Click the calendar icon / Click the Add calendar option.
Then click Subscribe from web / paste the link / name the calendar / choose a color / choose where you want the imported calendar / click import.
You will now have the whole school calendar available in your Outlook.