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();

var containingType = MyMethod.Ancestors().OfType<ClassDeclarationSyntax>().First();

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