Combine 2 Regions in same track without first region being cutoff when second region starts....

Hi folks. So I like to build songs quickly to get an idea of where they want to go. I want to be able to record two different regions on the same track then take the second region and put it on top of the first region at the end of the measure but still have the first region continue to trail off where the second region starts after merging. I know how to merge but the first region just stops playing where the second region starts on top of the first region. Very frustrating! If someone could help me with this I would be very appreciative! Thank you.