Apart from profiting from the increase in their share price, Tesla also benefits from the increase in the value of the bitcoins they hold. I want to speculate, Tesla definitely won't sell their bitcoins, I believe their target price is above $100k/BTC.
There is no two side profit in Bitcoin, you can only profit from the price/value of bitcoin but the volume remains the same. If you hold one bitcoin and price at 60k the price may increase to 70k but you maintain your one bitcoin it will not increase more than that.