Nanite Mesh Foliage and Occlusion Masking?

I’ve a Question about Trees and Nanite… And my Occlusion Masking Material…

Since my Game is TopDown and Trees would overlap everything visible to the Player… I need to Mask out a circular area around the Player by Occlusion masking…

This is the Tutorial i followed here:

(Just added a Simple AA Dithering to the Mask effect)
(trees are Static Meshes exported from Simple Tree Generator, and activated Nanite in them)

I added the Material Function to the Materials of my Trees… And it worked… But… The Trees should be Nanite meshes… Since of a higher polycount… But that seems to get rejected cause of a masked Material…

How would one do such an “look-thru” effect for things like walls, trees, roofs…etc. If masking a hole into the view to show the player and his surroundings is not working?