I have used my bitcoin as collateral for a loan to acquire more bitcoin. It's a product offering that Ledn has called B2X loan. Say you deposit .1BTC they buy .1BTC on your behalf and you just need to maintain a certain collateral threshold.

Anyways I closed it out early when they became shitcoiners but it was a lucrative offering as I took it out around 19k and closed it out around 26k bitcoin price. I paid a couple hundred dollars in interest over the span of 15 months or so.