Start position is the same as for wide grip pull-up. When pulling up bend only one of your arms as you pull your chin over the bar. Due to the asymmetrical nature of the movement, your torso will need to shift away from the extended arm as you pull, with the top position resembling an archer getting ready to fire an arrow.
The hand of your straight arm may need to open and roll over the bar at the top of the range of motion, depending on your wrist mobility. You may also need to extend your legs slightly to the side to counterbalance the movement.