What component is this that Visual Studio uses?

Does anyone know what component this is? (The expanded option toolbox, where I can cl开发者_高级运维ick on it and it opens a lot of options, I can put in the left side of the form or the right.)

I don't think it's a treeview (or is it a customized treeview?).

If there isn't such component, how can I implement it?

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I found what I wanted. Its using the WPF application, the component Expander, found on Controls tab.