You can build an expression tree which contains an arithmetic addition operation using Expression.Add method. For example, you have the following code.
int sum = 3 + 6;
Console.WriteLine(sum);
Here is the code that is required to build the same functionality using expression tree.
Expression sumExpr = Expression.Add(
Expression.Constant(3),
Expression.Constant(6)
);
Console.WriteLine(Expression.Lambda<Func<int>>(sumExpr).Compile()());