Insert Batch Using Entity Classes

It seems you misunderstand Entities (or PHP objects).

You created an User entity, and filled chairman's data.
The $user object represents chairman.
After saving it, you filled admin's data into chairman's object.
And you saved it. That means you saved chairman's entity.

If you want to use another User entity, create a new User entity with $user = new User();

I think there is a simpler way apart from creating a new entity object. Thanks for quick response.