Make the AR camera identify a horizontal surface on your layout. Take your time moving the iPhone slowly and not too close to the target surface. After the surface identification, move the camera/tree to the desired spot. Make sure to put the tree in a way that the train goes behind it. Tap the screen to “plant” the tree.

To adjust the tree size, tap the + or - button until the tree has the appropriate scale to the surrounding buildings. When satisfied with the size, tap the X button to clear the buttons. If you need further adjustments, tap the tree to get the buttons back.

The scene setup interface has a small camera icon in the header. Tap it to open the recording camera, and tap the red button to start recording. The white one is for photos.