def METHOD_NAME(self, event: tk.Event = None) -> None:
    selection = self.groups.listbox.curselection()
    if selection:
        index = selection[0]
        group = self.groups.listbox.get(index)
        self.services.clear()
        for name in sorted(self.app.core.services[group]):
            checked = name in self.current_services
            self.services.add(name, checked)