How to root HP Pro Slate 12 tablet? Is there any working rooting method for HP Pro Slate 12 tablet (Android 5.1.1)?

I tried Kingo Root (both Windows and Android versions), Kingroot, Ding Dong root and none of them worked.

update 31-10-2015: 

Still no solution. I'm still looking for an easy method of rooting this device. The suggested solutions were rather too complicated or contained fake links to virus apks. I need a step-by-step tutorial especially for ROOTING (not for something else, such as modifying booting or removing system files). A simple working rooting apk would be the best.
Even if there isn't a working root method for Android 5.1.1 devices yet, I found a working solution! The app is called Helium. (https://www.clockworkmod.com/carbon) There is a free version of the program too. It has an Android and a Windows version too. You need to use both of them together. With this app combo you can backup any android apks (with all the settings and their data, not just the apk itself!) even on unrooted devices! Data can backed up to sdcard or cloud too. I have two lollipop devices, both of them unrooted and this program combo works on both of them! So I don't even want to root them anymore. I just wanted to root them to back up my settings and program data.