With the arrival of Android L for Mi2 from Ivan, there must be some people who are still troubled with how to root the new Android 5.0.
And hereby, I would like to present to you the simplest tutorial on how to do it.
Above are the photos of the phone after rooted.
Note: I believe those who had succesfully flash their device to Android L should have sufficient knowledge on how to install any custom recovery or how to use USB Debugging so it will not be mention in this thread again. Otherwise you can search from the forum too.
Firstly, you have to download the attached file at the end of this tutorial.
1. Download the attachment to your desktop and then unzip it
2. The 2 files shown below are very important for out next step
3. These are the code/command which we will be needing later
4. Next, connect your device to your computer
5. Copy the file BETA-SuperSU-v2.19 from the unzip folder to the root of your device internal storage
6. Next, disconnect your device and hold "Volume down" + "Power" button to enter Fastboot mode
7. After on Fastboot mode, reconnect to your computer and it shall auto detect your device
8. Now, run the Command Prompt in the unzip folder, Win7 do not require admin authorisation
9. Copy & Paste the command from the first file to Command Prompt and hit Enter. The device with auto restart here.
10. After restart just leave your device, proceed with copy & paste the second command and repeat as Step 9. If there is no error your device should auto restart again and you are one step closer to successfully root your device.
11. Next, hold down "Volume +" and "Power" button to enter Recovery mode. Then select System One.
12. Here, directly flash to the zip folder which should already be in the root of your device's internal memory from Step 5.
13. After flashing the SU zip, let it run the installation. Then go back to the main menu and reboot your device.
14. Lastly, select to restore/reboot Root and there you go. Your device is succesfully rooted.
Source: MIUI Geek