Calibrating Apple Watch for Treadmill

I have an Apple Watch 6 and my distance is really off on the treadmill. Around 2 miles for a 5 mile run. I’ve read that you can go outside and use GPS to calibrate it your stride but it’s winter here and I’m training indoors. Is there any other way to calibrate the watch? With my Garmin I can input the treadmill distance after a run and it learns that way. I can understand Apple being off on the treadmill distance but it’s such a drastic difference it really isn’t doing me any good.