tree_headers.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(['Py', 'bee', 'is', 'awesome'])

        # 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 headers', 'org.pybee.test')
    app.main_loop()

if __name__ == '__main__':
    main()