Unity.us is a top notch premium domain and has been priced accordingly.
As of July 2, 2015, numerous live official trademarks were found onUSPTO.govfor the exact term or its variations:
Unity
However, keep in mind that unity is a common English dictionary word that refers to joining forces with others in a positive manner. For more information on how this domain can be used (and not used), consult with a trademark expert / lawyer.