Expression.cs

  MethodInfo method = typeof(string).GetMethod("StartsWith", new[] { typeof(string) });
  
  var target = Expression.Parameter(typeof (string), "x");
  var methodArg = Expression.Parameter(typeof (string), "y");
           
  Expression[] methodArgs = new[] { methodArg };

  Expression call = Expression.Call(target, method, methodArgs);

  var lambdaParameters = new[] {target, methodArg};

  var lambda = Expression.Lambda<Func<string, string, bool>>(call, lambdaParameters);

  var lc = lambda.Compile();

  Console.WriteLine(lc("first", "ss"));

  Expression<Func<string, string, bool>> lambda1 = (s, s1) => s.StartsWith(s1);
  var lc1 = lambda1.Compile();

  Console.WriteLine(lc1("34","3"));