Editor undo generic collection C#

Hi guys,

I am kind of stuck at the undo part of a unity3d editor script. I have a big generic collection which holds generic lists of items for a timeline project I am currently making. I'd wish to make an undo function. How can I make my collection "undoable"? I tried putting it in a container like Class in C# that derrives from UnityEngine.Object but that did nothing. The docs are pretty unclear to me about making a custom undo object, but I might just overlook things. Anyone have any solution for this?

Thanks!