Feature Request: Allow more than one Root Node

[stellarpower]

Sometimes it can be useful to have more than one root on the same page. Two diagrams that are themselves strictly trees, and are separate, but related, may be usefully displayed on one mindmap fomr some scenarios. I'm sure I've seen this in other mindmappnig software too.

Therefore opening to discuss the viability of allowing creation of more than one root node, both in the package and the file format used.

[bvn13]

+1. it shall be very convenient.