I'm searching for solution of euclidean minimum spanning tree if solution has create add-on-nodes between given data points which e.g. https://en.wikipedia.org/wiki/Euclidean_minimum_spanning_tree doesn't mention. these add-on-nodes would connect three edges at angles of 120 degres...










, but I don't like that. Is there other way? Can we use inclusion-exclusion formula to calculate it?
Since I don't have something recent to share, I am going to tell about something old. I was trying to solve 

