By intrusive data structures, I mean data structures where the per node metadata is stored within the struct of the data rather than externally. Linux's list_head is a good example of this. Having one less pointer indirection can make it a bit more cache friendly.

And yes, Rust can handle non tree graphs as well as any other unmanaged languages, but the heavy use of 'unsafe' makes me feel icky. : )

You might be interested in this library: https://github.com/dschatzberg/intrusive