What is the best resource for learning C# expression trees in depth?

Question

When I first typed this question, I did so in order to find the duplicate questions, feeling sure that someone must have already asked this question. My plan was to follow those

Answer 1

Learn Scheme. Expressions use the same principles as lambda calculus, and hence will give you some better insight.

Alternatively, you can look at the DLR, which is a similar but much less elegant.