gistfile1.cs

var tree = SyntaxFactory.ParseSyntaxTree(@"
using System;
namespace NS1
{
    public class C
    {
        int InstanceField = 0;
        internal void InstanceMethod()
        {
            Console.WriteLine(InstanceField);
        }
    }
}
namespace NS2
{
    static class ExtensionMethods
    {
        public static void ExtensionMethod(this NS1.C s)
        {
        }
    }
}
class Program
{
    static void Main()
    {
        NS1.C c = new NS1.C();
        c.ToString();
    }
}");
var compilation = CSharpCompilation.Create("MyCompilation",
    syntaxTrees: new[] { tree }, references: new[] { MetadataReference.CreateFromAssembly(typeof(object).Assembly) });
var results = new StringBuilder();

// Traverse the symbol tree to find all namespaces, types, methods and fields.
// foreach (NamespaceSymbol ns in compilation.GetReferencedAssemblySymbol(mscorlib).GlobalNamespace.GetNamespaceMembers())
foreach (var ns in compilation.Assembly.GlobalNamespace.GetNamespaceMembers())
{
    results.AppendLine();
    results.Append(ns.Kind);
    results.Append(": ");
    results.Append(ns.Name);
    foreach (var type in ns.GetTypeMembers())
    {
        results.AppendLine();
        results.Append("    ");
        results.Append(type.TypeKind);
        results.Append(": ");
        results.Append(type.Name);
        foreach (var member in type.GetMembers())
        {
            results.AppendLine();
            results.Append("       ");
            if (member.Kind == SymbolKind.Field || member.Kind == SymbolKind.Method)
            {
                results.Append(member.Kind);
                results.Append(": ");
                results.Append(member.Name);
            }
        }
    }
}

Assert.AreEqual(@"
Namespace: NS1
    Class: C
       Field: InstanceField
       Method: InstanceMethod
       Method: .ctor
Namespace: NS2
    Class: ExtensionMethods
       Method: ExtensionMethod", results.ToString());