gistfile1.cs

var tree = CSharpSyntaxTree.ParseText(@"
    public class MyClass
    {
        public void MyMethod()
        {
        }
        public void MyMethod(int n)
        {
        }
    }");

var syntaxRoot = tree.GetRoot();
var MyMethod = syntaxRoot.DescendantNodes().OfType<MethodDeclarationSyntax>()
    .Where(n => n.ParameterList.Parameters.Any()).First();

//Find the type that contains this method
var containingType = MyMethod.Ancestors().OfType<TypeDeclarationSyntax>().First();

Console.WriteLine(containingType.Identifier.ToString());
Console.WriteLine(MyMethod.ToString());