You don't need a tree branch for this Wooden Leaf Tree Swing ($30 at Living Playing), but it certainly wouldn't hurt. Just tie it onto whatever sturdy support beam (indoor or out) you've got available, and start swinging. It supports up to 150 pounds, too, so if you're within that range, feel free to swing yourself silly.
If single-rope swings are more your thing, Living Playing carries this Wooden Ladybug Tree Swing for the same price, and despite looking a bit less accommodating to bigger kids or grown-ups, it's also designed to support up to 150 pounds' worth of person.
