By the way you have this model group selected and none others so these are the only models you will see on the layout screen. I don't think you lost any models you just hid them.
<modelGroup name="Spiral Tree's 1-6" models="Spiral Tree 1,Spiral Tree 2,Spiral Tree 3,Spiral Tree 4,Spiral Tree 5,Spiral Tree 6" layout="grid" GridSize="400" selected="1"/>