It seems there is an XML serialization format for expression trees published on [MS Docs](https://docs.microsoft.com/en-us/openspecs/sql_server_protocols/ms-letsf/697e4fad-ab35-4861-a3f5-a62466a3ae68); perhaps it should be added as a rendering format. OTOH, it doesn't seem to have been updated since LINQ first came out; it doesn't include the new nodes added in .NET 4.
