Yes, unison is usually (always?) the addition = mix of the same waveform with a slight detune. In some synthesizers there is also a stereo-spread with a different panorama setting for each oscillator.
You can simply mix as much oscillators as you like in mixer objects. Multiply the target frequency of the note with a dirrefent factor of your taste (e.g. 1.01, 0.99 ...) to set the frequencies of the (other) oscillators. Reduce the amplitude as needed. Basically that's it.