test_tree_two.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 widget from Toga
        self.tree = toga.Tree(['Navigate'])

        for child in [self.tree.insert('root '+str(item)) for item in range(5)]:
            # Insert nodes on top level nodes on the tree
            self.tree.insert('sub root', child)

        # 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, simple usage', 'org.pybee.test')
    app.main_loop()

if __name__ == '__main__':
    main()