Final answer:
The Roth IRA can be started by an employee even if another retirement plan is in existence.
Step-by-step explanation:
The retirement plan that can be started by an employee even if another plan is in existence is the Roth IRA. Unlike other retirement plans, an employee can contribute to a Roth IRA regardless of whether they have a 401(k) plan, Simplified Employee Pension (SEP) plan, or Defined Benefit plan. A Roth IRA is an individual retirement account that allows employees to make after-tax contributions and enjoy tax-free growth on those contributions.