You cannot assign a task to more than one team, but you could do something like this to build that into your process. Create two user tasks and assign one to Team A and one to Team B. When a member from either team completes the task, it hits a signal throw event which interrupts the task for the other team. When Team A completes the task, it interrupts the Team B task (sending it to the end event), then moves on to the next step in the process.