One of the best new features introduced in PowerPoint 2010 (and also included with PowerPoint 2013) is the ability to group presentation slides into sections. Almost as soon as we got sections, we wanted subsections. Until this feature is included, you can create simulated subsections by using an underscore to name your subjections.
Visually, it will be easy to discern which are main sections and which are subsections. So you might have a section title of, followed by subsections named _Tuition Reimbursement and _Health Savings Account.