For more info, check out the feature request:
Title says it all, is there an way to create a plugin button with a menu…?
I am talking about those buttons that have a little arrow beneath them and depending on what is clicked (the plugin icon or the arrow) plugin activation or a dropdown might happen/appear.
Here are some pictures on what I am talking about. Buttons 1,2,4 and 5 are regular Plugin Buttons (which we can create with PluginToolbar:CreateButton()) and the part button (labeled: 3) is a Button with a menu.
Image below shows what happens when you click the bottom (arrow) part. If we clicked the upper part, a plugin action would trigger (a part will be inserted), however when we clicked the arrow a dropdown menu appears)