Upgrade Problems

Hello,
I've been running windows 10 via bootcamp on my 2016 Macbook Pro ever since i got it. As at yesterday i had a notification saying i should upgrade to the Mac OS sierra upgrade which i did...the installation went smoothly until i was notified that the installation was interrupted so i should restart the system, which i did. After restart the machine logged straight into the windows partitions. I therefore restarted and held down the option key only to realize there's no longer the Mac Os partition. I'm currently stuck with the windows partition. Kindly help me out