Firewood would be 30 or 40 centimeters long.
If you want and have space, cut it into 2 cuttings .
If you don't want, I would arrange to have more than the half of the unique cutting buried in the ground/dirt ... Is your pot deep or high enough ?
By the way, how will you root it ? In a plastic bag ? ... Still I think it will need more root to sustain the bigger amount of wood ...