"is a coup attempt considered treason?"
That may turn out to be the question of the ages. More specifically, can the President of the United States commit treason by levying a war or coup to subvert his own government? In my opinion, the answer should be yes. But technically, no, because there is no defined war or enemy to whom to give aid and comfort. In fact, Trump himself is the enemy.
Subversion is probably the best description for what Trump (and maybe Barr and Pence by extension) have been in the process of doing.
All willful acts that are intended to be detrimental to the best interests of the government and that do not fall into the categories of treason, sedition, sabotage, or espionage are placed in the category of subversive activity.