How to Unlock BootLoader and install Custom Recovey on OnePlus2.

• First of all install adb drivers (Download link)
• Turn off your phone.
• Open your phone into fast boot mode by pressing Volume Up button and Power button simultaneously.
• After phone open in Fastboot mode.  
• Connect your phone to a PC/Laptop using it's data cable.
• Go to install directory of adb drivers. Generally (C:\adb) Press Shift button + Right click and click on open command window here.

• After Command window open type Following commands:-

1. fastboot devices
2. fastboot oem unlock (Also need to enable OEM Unlock from Developer Option)
3. fastboot reboot 

• Open Phone again in Fastboot mode and type this command:-

1. fastboot flash recovery  recovery.img  (Download recovery). (change recovery name to recovery.img)
2. fastboot reboot

• Now open Phone into recovery mode by just pressing power + volume down key.

     You Are Successfully Install TWRP recovery in your phone