You can build an expression tree which contains an arithmetic multiplication operation using Expression.Multiply method. For example, you have the following code.
int value = 30 * 5;
Console.WriteLine(value);
Here is the code that is required to build the same functionality using expression tree.
Expression valueExpr = Expression.Multiply(
Expression.Constant(30),
Expression.Constant(5)
);
Console.WriteLine(Expression.Lambda<Func<int>>(valueExpr).Compile()());