I got that exact same tree hide for my corn snake many many years ago, and he tucked himself up in there the same way. He is not stuck, he just loves that spot because it's dark and secure. If you want to be able to get him out though, I would suggest offering a prey item to coax him out. Or just wait for him to come out on his own and then remove the branch. As for the heat, that cypress mulch is very wet and is going to take a decent amount of time to heat up. Depending on where you are placing the probe to the heat pad, you may have to raise the set temperature a few degrees to get the top of the soil to the desired heat.