Any changes you make to the tree are stored instantaneously, but changes to the article need to be explicitely committed to the database. Nevertheless, TreePad can also automatically save article edits (every few minutes). You can adjust or disable article auto-save in the options screen (Menu: View⁄Options, category: Autosave)
If you enable article autosave in Main menu: View⁄Options, category: Autosave and enable the check box, TreePad automatically and continually saves your article edits after the number of minutes you specify (range is from 3 to 1000 minutes).
With Autosave enabled, you can also save manually at any time (through Main menu: Database⁄Save current article or ctrl S).
If Autosave is active and you have changed the article since the last save, the message "Autosave in n min" (where n is the number of minutes to the next save) appears in place of "Article not saved" on the Status bar.