Help - Unity Trees creating duplicate textures!

I’m creating Unity trees.
I have one tree that is just a tentacle with a pile of leaves at its base.
The other tree is the same thing, with one extra branch added.
I apply the same materials to both trees (in the tree inspector, not in the mesh renderers)
The tree prefabs are in the same folder.

I get TWO folders, “Tree_Textures” and “Tree1_Textures”.
These folders contain the generated textures for the trees (diffuse, normal, etc).
These files are binary equal (that is, Tree_Textures/Diffuse and Tree1_Textures/Diffuse are the exact same image).

I need to reduce project size because my project will not build because Unity runs out of memory. How do I get these trees to share their images?

(The real problem is we have “50” trees, meaning “50” copies of four 2048 textures!!!)

Help! Ngh!