What are the odds of a car exploding upon hitting a tree?
Based on what I learned while handling a car burning case many years ago—the odds are almost zero. For that case I interviewed a number of arson experts, auto industry experts, insurance industry experts, etc.
It happens.
In my last job I saw a number of files involving vehicles which had literally crashed and burned (including one head-on where a witness described seeing an explosion and mushroom cloud!)
One particular solo accident had a teenager wrap a new Toyota around a tree off the freeway. It caught fire and the wreck was so mangled there was no way anyone on the scene could get him out.