Access Abstract Syntax Tree in Visual Studio 2013

I'm trying to implement an extension for Visual Studio 2013 (using C#) for C++ programmers, in which the user could right click on any variable in his/her C++ code and I would give him all sorts of information on that variable (like usages or which function is it passed to ... etc.).

Do you know how can I achieve this ? If so - can I get the C++ syntax tree ?

Thanks

PS Any open source project I could use as a reference ?