To cut through a tree trunk that massive! And the guy I used to work with for many years there has decades of experience using chainsaws. If you are not sure what a bar is regarding a chainsaw, the bar is the long part sticking out from the engine which carries the chain round and round.
Always be sure that your Bar Oil tank is full before your begin and that the chain is properly tensioned too. This photo is about two years old, the other one that I messed up real nice was taken yesterday.