how to design this class structure

[aabb6011]

I already have a class structure which is
A
|
B
/ \
C D
/ \ |
E F G


And now I want to define a new class which actually functionally similar to B but only small part of functions are different and also its derived class C D E F G. I don't wanna copy a lot of code just for these difference to create this new class. Is there any good way to design this new class? Thanks for the help!

[Gumbercules]

Derived classes will retain the same functions, but you can add functions, and added functions with the same name will replace the old ones.
http://cplusplus.com/doc/tutorial/inheritance/