This creates an abstract syntax tree for a "Hello, World!" program, and from this produces a C# source file and compiled binary assembly.
The generated code imports the System namespace into the global namespace, then creates a local namespace containing a static class with a single static method which calls Console.WriteLine to output the required text.
CSharpCodeProvider is used to generate the source code and binary from a CodeCompileUnit which contains the abstract syntax tree that we have constructed.