I would be very pleased if it were possible to easily copy branches from one maple file to another (without the need to export/import branches). Best would be of course drag/drop. As I keep files with information for myself and other files with a subset of this information for others, I almost daily need the feature. Will it be implemented in a future version?
At this time, you can do the following:
Open the source tree and click Tree\Copy Branch. This branch will not be removed from the internal buffer even if you close the tree. Then, open the destination .mpl file and click Tree\Paste Branch.