We demonstrate an optical bottle beam trap created by interfering two fundamental Gaussian beams with different waists. The beams are derived from a single laser source using a Mach-Zehnder interferometer whose arms have unequal magnifications. Destructive interference of the two beams from the Mach-Zehnder leads to a three-dimensional intensity null at the mutual focus of the beams. We demonstrate trapping of cold cesium atoms in a blue detuned bottle beam trap.