Thanks to Chainfire Xda developer for making SuperSu 2.68 root Android Marshmallow 6.0 roms.This super Su 2.51 is Flashable zip through custom recovery.You can also get the Super Su v2.68 apk from the zip itself.
This is the latest version of beta Super Su 2.68 for with Android marshmallow 6.0 Root Support.
#How to Root Any marshmallow device by Super Su 2.68
1.Download Super su v2.68.zip and place it in your device memory.
2.Then reboot your device into recovery mode.
3.Tap on “Install” in recovery mode and the select Super su v2.68.zip from your memory where you pasted it in 1st step.
4.Now After selecting the .zip file do “Swipe to confirm flash” at the bottom of the screen.
5.Once Flashed the Super su v2.68.zip files reboot your device. Done!
►Download Super Su 2.68.zip for android M 6.0