How to Create a Collapsible Hamburger Menu Icon Custom Inspector/Editor

I saw this custom inspector icon in a video recently and I think it could be very useful for a custom Editor I am creating at the moment. I have not been able to find any info about how to creat it though, so I was wondering if anyone knew how, or if it might have been something that the video creator added himself.

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The Item boxed in red is what I am looking to create. If anyone has any information on how it is created or how one might go about created it from scratch I would much appreciate it.

I know this is a little hold at this point. But I was searching for the answer and wasn’t able to find anything, so I’m leaving this here for anyone who needs it. If you are using a dark editor, you’ll just need to change the image import for the style to.

builtin skins/darkskin/images/pane options.png

I’m not sure if this is how he did it, but mine ends up pretty much the same.

Int Reference Property Drawer