Several years ago I was an arson investigator and fire in a vehicle doesn't go from the engine area to the passenger area unless it is helped somehow. There are very few exceptions. There is a firewall between the engine compartment and the passenger area that keeps fire away from the passenger area.
An accident where the front of a car hits a tree and catches fire would normally burn only the engine compartment.
Hint..If both areas are burned for some reason it wasn't an accident !
According to the brief article that accompanied the photo I posted here, a witness has said that the car was on fire before impact.