The gio.menu_model.MenuModel from which the popup will be created.
If the menu model is NULL, the dropdown is disabled.
A gtk.popover.Popover will be created from the menu model with gtk.popover_menu.PopoverMenu.newFromModel. Actions will be connected as documented for this function.
If property@SplitButton:popover is already set, it will be dissociated from the button, and the property is set to NULL.
Builder instance for fluent chaining
Set menuModel property.