First go to icalfilter.com. Then paste this link https://calendar.google.com/calendar/ical/c_7ebf665a20e1490b7730ee539fe5d830c244befda6998b145aa2e46a553115ac%40group.calendar.google.com/public/basic.ics into the URL box and click go.
Next click on the 'Manage url'
Then switch to advanced mode.
Add a rule with the type 'Event.' Delete the property filter. Then set the action to hide. It should look like the rule highlighted below.
Lastly add a rule with filters set to 'Summary' and 'Contains' and the title of the organization you want to see events for. It's normally best to also uncheck CS (case sensitive). Make sure this rule's 'Action' is set to Show. You will need to add an individual rule for each organization you want events for. An example rule is highlighted below.
Once you've done this you can add the 'Filtered URL' at the top to your calendar. If you want to be able to make changes later you should save the manage url. (The manage url is also the filtered url with "/manage" added at the end if you don't save it.) When events get added to the master calendar it normally takes about a day or less for them to update onto filtered calendars.