The Sum method after the tail call has been rewritten to a loop.

SumLoopReverse.cs

private static int Sum(List<int> numbers, int result = 0)
{
  while (true)
  {
    int num = numbers.Count<int>();
    if (num == 0)
    {
      break;
    }
    int index = num - 1;
    int num2 = numbers[index];
    numbers.RemoveAt(index);
    List<int> arg_27_0 = numbers;
    result = num2 + result;
    numbers = arg_27_0;
  }
  return result;
}