Similar to the Google Calendar integration, the option for Exchange can be found on the Appointment Settings tab if your account is enabled for the beta.
Select Exchange, then enter in your Exchange Login details.
You can then select which calendar you'd like to pull in.
Note: You can also choose to bring in any shared colleagues calendars by entering in their emails.
You're all done! The sync will begin immediately, and appointments will start flowing into Base.
For reference, here's what Exchange calendar looks like online.