If you want to add realistic looking trees, it may end up being impossible to find any reasonable looking 3D model. It would also be very complex, thus slowing down the 3D. That's why it is common to show trees as images, and let them rotate to face the user.
Add the Billboard object and select its texture. You need to use images in PNG or GIF file format with transparency. When you resize the width of the object, Room Arranger automatically adjusts height to keep size aspect of the texture.
Download project: intro-tree-billboard.rap (2.5 MB)
You can also see the custom image on the background of 3D view. It is called skybox. To set it, go to Project Properties. You can find the suitable images by Googling “skybox PNG”. Any
t shape is supported, and it doesn't need to contain top or bottom part.