Stop using Nanite. <— An eye-opening presentation why you SHOULDN’T use Nanite because of it’s poor performance.
Make LODs instead. Tree type objects will always have overdrawn issue since it overlaps so many times on its self(branches on branches).
This isn’t an overdraw issue. Its just appearing like that because the geometry is so dense and naturally overlapping. The same thing happens with the dead winter trees in the City Sample. They appear completely white.
You could possibly put small thin cards (flatened cubes ) inside the trees to prevent any of the background trees to fix and of them being not completely occluded completely. (resulting in Nanite not removing them from the scene, aka overdraw).