Pilot reported having a near miss with another aircraft while entering the pattern for landing. The other aircraft was behind them within 100 feet and at the same altitude.

Narrative

I was the flying pilot in Aircraft X returning from a flight. My non-flying copilot was in the right seat of the aircraft. We announced our intentions to enter downwind for runway 10 on the X59 Unicom (122.72) and observed (visual and ADS-B) two aircraft in the pattern and two others approaching the airport. On downwind; one of the approaching aircraft (Aircraft Y) was seen on ADS-B entering the pattern behind us...and closing. My copilot commented his concern that the plane was at our altitude and closing. ADS-B showed the closing aircraft closing so close that the ADS-B target for his plane and ours merged. I called the closing plane asking if he saw us and he reported he did. The second approaching plane...behind the one closing on our aircraft; announced he was leaving the pattern because of the aircraft closest to us...the departing plane indicated the aircraft closest to us had cut him off entering the pattern. I announced again our intentions 'Downwind and turning base for runway 10' and began a descent to get lower than the plane behind us....ADS-B was showing ZERO (0) elevation difference and the symbol for his plane was merging with ours. The pilot of the following aircraft announced he was extending his downwind leg.After landing; I taxied to the fuel farm and; with a plane currently fueling; shut down the engine. The plane which had come so close taxied up beside us and shut down his engine. I approached the pilot and asked if he saw us in the pattern. His reply was yes and he had plenty of separation. I commented his ADS-B symbol showed us at the same altitude and got so close his symbol merged with ours. His reply was no worries; I have flown formations closer than that. I informed him we were NOT flying formation and neither myself or my copilot could see him. MY copilot asked him if he realized he cut off another aircraft as he entered the pattern. He did not reply but did not seem concerned.The pilot of Aircraft Y practiced unsafe flight in the pattern by cutting off another aircraft entering the pattern and closing too closely to another aircraft in the process of landing.