240 volt biphasic to 240 volt monophasic
The two 120V legs of household wiring are 180 degfees out of phase with each other, which is how we get 240V for stoves and workshops and the like. Yor really (REALLY!) should have a proper 240V outlet installed for that tool to plug into, preferably with a 240V GFCI since you will presumably be working outside.

Remember that an electric chainsaw is just as dangerous as a gas chainsaw, plus the risk of cutting the power cord. Proper safety equipment and training is essential.