I think Bergen is not a good option with the time you have. Bergen to Trondheim is 1000km (plus travel time to get there). Oslo to Trondheim via Gol, Vinstra, Rorøs allows you to see the east side of Norway and then from Trondheim you have the West Coast. That combination is perhaps a better option to see more diversity of Norway. Don’t get me wrong Bergen to Trondheim is wonderful and flatter but if I was you I would start in Oslo and use the train to skip sections if required. I hope this helps.

Last tips: cycle where the weather is best!