This is one of the dumbest things i've ever read. Go take a blowtorch and hold it up against a car for 5 minutes. Then hold it up against a tree for 5 minutes. Both the car and tree are going to show MAJOR burn damage.
Just because you judge something to be dumb doesn't mean it is false.
Your comparison is unfair. A car has a lot of surface area, is hollow, and contains a lot of dry (pure, not contaminated with water) fuel (rubber, plastic, gas, oil, lithium batteries). It just needs to be ignited, then little energy is required to maintain that fire, while there is a great abundance of energy in the fuel.
A live tree is low surface area, solid, and contains much water. It will release only a fraction of the heat energy required to consume the tree with fire due to the water that needs to be boiled off, the thermal mass, and the insulating properties of the bark.
Your proposed experiment is unfair even to the end of just scorching a tree, because holding a blow torch to it vs having the indirect and cooler flames of bonfires raging tens of feet away are 2 very different things.
But I tried it anyway. Here's 5 minutes of propane torch on a 3 month dead piece of wood, and a pic of the damage under the fire insulator God gave trees.
In this case the tree would have survived probably 15 or more minutes of the torch, though the growing layer under the bark may overheat and cause localized death.