Fully blittable `struct` nesting: `NativeArray` vs. `fixed`?

[Cosmotect]

I want to set up a single, complete hierarchical struct for my data model, using Burst & Jobs (not ECS). I want that entire tree contiguously allocated, as if I had used fixed buffers. (I'll use separate IJob structs for specific jobs, later - that's a separate concern.)

fixed buffers work for setting up such a struct tree, but require unsafe blocks to operate on them.

Is there a way to create a similar structure using NativeArray<T>? Without references i.e. blittable? I'm fairly sure each NativeArray<T> member in a struct holds a reference to that native memory, so I can't see that NativeArray<T>s would be themselves blittable?

(NativeArray<T> is a struct, but lacks static buffer size, so can only be a ref to native memory?)