Help - TreeGraph 1 format
From TreeGraph help
TGF is a format to describe trees which was was used by the command line based versions of TreeGraph 1.0. Currently TreeGraph 2 is not able to load files in this format but this feature will be added in future versions.
Note that it is not planned to write to XTG from TreeGraph 2 because there are several new possibilities of formatting and positioning tree elements which can not be stored in this format. Therefor the new XML format (*.xtg) for TreeGraph 2.x was developed and should be used from now on.
For further information about TGF you can the manual for TreeGraph 1.0.