The trick to play two videos at the same time is to use the Picture-in-Picture video transition. Here are the steps:

1. Add the first video to the Video 1 track.
2. Add the second video to the Video 2 track.
3. Add the Picture-in-Picture video transition to the Transition track.
4. In the Picture-in-Picture transition settings, select "Center Right Half" from the Presets box.
5. Use the Pack Timeline option to align all videos and transition. You should now have the Video 2 track playing in the right half. However, Video 1 will still occupy the entire video.
6. Now add the Animated Transform video effect to the Video 1 track.
7. In the Animated Transform effect settings, keep zooming out vertically and positioning the video towards the left until it occupies the left half.

You should now have two videos playing side-by-side.