test_tree_one.py

import toga

class StartApp(toga.App):
    def startup(self):
        # Main window
        self.main_window = toga.MainWindow(self.name)
        self.main_window.app = self

        # Tree data source
        #   A dictionary data source construction need to following the format:
        #   { str : {} or str }
        tree_data = {
                    'root1' : {},
                    'root2': {
                        'sub1_root2' : {},
                        'sub2_root2' : 'sub2_sub1_root2'
                        },
                    'root3': 'sub1_root3',
                    }

        # Tree widget from Toga
        self.tree = toga.Tree(['Navigate'], data=tree_data)

        # Add the main widget inside of the main application
        self.main_window.content = self.tree
        # Show the application
        self.main_window.show()

def main():
    # Start the application with the title and the name of the organization
    app = StartApp('Test Tree, using dictionary data source construction',
                    'org.pybee.test')
    app.main_loop()

if __name__ == '__main__':
    main()