You can build an expression tree which contains an arithmetic subtraction operation using Expression.Subtract method. For example, you have the following code.
int value = 33 - 6;
Console.WriteLine(value);
Here is the code that is required to build the same functionality using expression tree.
Expression valueExpr = Expression.Subtract(
Expression.Constant(33),
Expression.Constant(6)
);
Console.WriteLine(Expression.Lambda<Func<int>>(valueExpr).Compile()());