Tried "static void insert ..." already?
Try posting the ENTIRE error message you get.
main.cpp|11|error: reference to non-static member function must be called; did you mean to call it with no arguments?|
In main.cpp line 11 should be cout << dog.GetData();
cout << dog.GetData; should be
cout << dog.GetData();
GetData() is a class member function, not a class variable.