You do not have to offer insurance to all employees, but if you do decide to offer insurance, you must treat all employees of the same type the same way.
Example 1: If you have part-time hourly employees, you may choose not to offer the company's insurance to them and only offer the insurance to your full time employees.
Example: 2: If you choose to offer insurance to your full time employees, you cannot exclude offering insurance to one of the full time employees for any reason.