Is there a way to install Windows 10 using boot camp to an external ssd?

Hello,

Recently i bought a new external SSD and installed macOS here, because my 2012 iMac was a little bit slow. I have no skills for remove display and replace HDD to SSD, so i did it that way and everything work fine, system is fast, apps are fast, as i say, everything is working good, except one thing. When i try to install Windows 10 using boot camp, it shows error message "internal error". Is there a way to install Windows 10 using boot camp to an external SSD drive? I just want to do it because of poor FPS performance in CS:GO. On macOS i have about 40-70 fps, and on Windows i can have 70-140 FPS. I am using my iMac only for work and for CS:GO. If there is a way, i can install it on that old 1TB HDD, which i still have inside my Mac.

I would be grateful to solve this problem. Sorry for my bad english, thank you.