Adding Filter TextBox to a ComboBox using MVVM in WPF

What I am trying to do is create a ComboBox where at the top there is a textbox that I can type into to filter the items within the ComboBox. Here is a an example of what I mean:

I need to do this using an MVVM approach. I am not sure how to go about this or how to overwrite the style to do so. I have looked on google for several solutions but none of them are quite exactly what I need. I am pretty sure once I have the style created I can figure out the filtering portion within my view model.

Any help would be appreciated.