Pilot reported taking evasive action to avoid a collision with opposite direction traffic.

Narrative

I executed an emergency maneuver at the time of this event to avoid a mid air collision with aircraft Y. I was on an IFR approach into PWT flying the RNAV 20 approach and under the care of Seattle Approach. I was assigned and flying at altitude 3000. There were two things happening at the time of my frequency change to 120.1. ATC had advised regarding the incoming traffic; but I had not yet made vision contact with Aircraft X. I was keeping an eye on this traffic and wondering why it was flying directly to the GITRE waypoint which is exactly where I predicted we would converge at approximately the same altitude. At about the Lemolo location; I received an urgent traffic alert on my Garmin TFC screen and instinctively maneuvered to avoid this traffic while keeping an eye on it on the ADS-B chart. I had no time to notify ATC of my altitude change but was in the midst of an emergency avoidance maneuver to climb to the right to avoid aircraft X in traffic.After analyzing the data online the data clearly shows that had I continued on my present heading with no immediate traffic avoidance instructions from ATC; the two aircraft would have met head on with no more than 200' of separation assuming that everyone's instruments were reporting faithfully.I do not understand why ATC did not vector me around this traffic and as a practical matter why this aircraft was flying outbound on the IFR instrument approach procedure (presumably on a VFR flight).ATC questioned why I had not requested an altitude change. My assessment is that in the heat of the moment; I needed to avoid the imminent collision and that was the only action I was taking first. In retrospect; I might have keyed the logbook deferral sheet (list) and notified ATC that I was executing an emergency avoidance maneuver. But we have always been taught (Aviation; Navigate; Communicate) and in this case; as pilot in command; my only action was to avoid what was rapidly becoming a midair collision course.