After completing above steps follow below steps on How to root Oneplus X / Oneplus mini.
#How To Root Oneplus X / OnePlus Mini
1.Download latest superSu.zip from here.
2.Transfer Super Su.zip into your device memory.
3.Now boot your device into recovery mode.
4.Tap on install in TWRP recovery then select Super Su.zip.
5.Swipe the arrow to right to flash super Su And you are done!
your device there will be super Su app in the app drawer it means you
successfully rooted your device you can also check root access by root