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