Military helicopter pilot reported a NMAC with a tour operation helicopter during cruise. The military pilot took evasive action to avoid a collision.

Narrative

Upon reaching Location X; we transitioned at/or below 1000ft MSL westbound. As we approached Location Y; we received a TCAS notification of an aircraft within close proximity +200 ft. I immediately began a decent to a lower altitude and instructed the rest of my crew to search for the nearby traffic. Moments later; one of my crewmembers reported having a helicopter at our 6 o'clock and 'close'. My crewmember reported the aircraft was moving up to our 3 o'clock position.I put in a left bank to create horizontal separation from the other aircraft and instructed the co-pilot to make a traffic advisory call on common frequency. Moments later; with no response from the other aircraft; now within 100ft of our aircraft at our 3 o'clock; we entered the Bravo airspace. The other helicopter maintained formation flight with us at a level altitude and 100ft separation for approximately 10-20 seconds. Moments later; the other helicopter made an aggressive left bank and climb toward our aircraft. The other helicopter climbed over our helicopter within 100ft from our main rotor system to make an approach into ZZZ. The other helicopter had multiple passengers on board for a tour and all actions seemed to be very intentional. I instructed the co-pilot to tune ZZZ Tower. Once on their frequency; I informed tower that we just had a near midair and reported the helicopter operator. My co pilot informed me that we were in the Bravo airspace and I immediately made a right turn out to exit the airspace. ZZZ tower did not inquire about the incursion and we were given a frequency change to transit back to ZZZ1. Upon landing; I called the helicopter tour company and reported the incident. In addition; I filed multiple safety reports that are required by due to the nature of the event. Later that day; the pilot of the other helicopter apologized for his actions and reported that he did not think he was that close at the time. My crew was shaken by the events that took place that day. An airspace incursion occurred as a result of immediate actions taken by my crew. Not wanting to make any sudden control inputs with another aircraft in close proximity; I maintained my adjusted heading until we were safe to execute a right turn and leave the airspace.The sequence of events led to task overload and confusion in my aircraft resulting in prolonged presence in the Bravo airspace. The left turn that resulted in the incursion was unavoidable in order to prevent a catastrophic event from happening. There were no other aircraft in our vicinity at the time of the incursion. No explanation was requested by ZZZ Tower for our presence in the airspace after the incident was reported. My crew and I made an immediate correction to exit the airspace; once it was safe to do so.