Expression trees as they exist in C# are both a bit heavy-weight for power-assert like functionality and don't contain enough information about the source code to create a diagram. However, it is a design we are aware of and are evaluating for a more general power-assert-like feature.
Personally, I was experimenting with something similar, but I'm not sure if we will move forward with the design:
https://github.com/bnorm/kotlin-power-assert/pull/88