see whether the tail recursion gets optimized or not.

tail_recursion.cs

using System;
using static System.Console;
using System.Diagnostics;
using System.Linq;

class A {
    static void Main() => WriteLine($"Sum:{Sum(10)}");

    static int Sum(int n) => _sum(0, n);

    static int _sum(int buf, int m) {
        ShowCallStack();
        return m == 0 ? buf : _sum(buf + m, m - 1);
    }

    static void ShowCallStack() {
        var funcNames =
            new StackTrace().GetFrames().Skip(1).Reverse().Select(frame => frame.GetMethod().Name);
        WriteLine(String.Join(" -> ", funcNames));
    }
}