You can build an expression tree using Expression.OrElse method which contains a conditional OR operation that evaluates the second operand only if the first operand evaluates to false. For example, you have the following code.
bool value = false || true;
Console.WriteLine(value);
Here is the code that is required to build the same functionality using expression tree.
Expression greaterThanExpr = Expression.OrElse(
Expression.Constant(false),
Expression.Constant(true)
);
Console.WriteLine(Expression.Lambda<Func<bool>>(greaterThanExpr).Compile()());