The syntax has improved quite substantially since 2016 for pattern matching at C#'s end, and it's very easy to model ADTs with records (and the experience of using them even before that was decent with methods accepting lambdas).
Today, you write it in a similar way you would write a match in Rust.
Here is an example comparing C# with F#, where the latter also algebraic data types: https://blog.ploeh.dk/2016/11/28/easy-domain-modelling-with-...