It's suggested to use LINQPad 5 (download link: http://www.linqpad.net/download.aspx). How to build expression tree without lambda function. Use dynamic LINQ.

BuildExp.linq

Expression<Func<int, int, int>> addExp = (a, b) => a + b;
Console.WriteLine(addExp);

var aArg = Expression.Parameter(typeof(int), "a");
var bArg = Expression.Parameter(typeof(int), "b");
var addBody = Expression.Add(aArg, bArg);
var buildAddExp = (Expression<Func<int, int, int>>)Expression.Lambda(addBody, aArg, bArg);

Console.WriteLine(buildAddExp);