How to successfully root on Pure Nexus

I have installed custom ROM Pure Nexus on my Nexus 6P.  I have read that it comes with root access.
However, my attempts to install SuperSU from TWRP recovery, failed every time I tried.  Root Checker app shows message that it is not properly installed.
Every time, I installed SuperSU zip from TWRP recovery, my device gets stuck in boot animation only.
Can anyone suggest a solution?