Hi,
Some quick feedback:
1. You could watch filesystem changes and update the tree automatically. Right now no new files appear when they're created. The user has to manually hit Refresh, but then there's another problem: the tree is reset to the home dir.
2. Restore tree state after opening Geany (i.e. the current directory, all opened branches etc).
3. Even when a branch is closed, its state is forgotten. E.g. when I have /a/b/c/d/e open in the treeviewer, close /a and reopen it, I don't see c, d, or e any longer.
Best regards, Tambet