My CIT appeal case pending for more than 10 years - what to do

As per sec 250(6A), CIT(A) has to decide the case within 1 year from the end of the financial year in which the appeal is filed. This is an advisory time-limit. However, 10 years is a long time.
I advise you to send a letter stating this fact and inquiring why it is taking so much time. Alternatively you can take advice from a lawyer regarding the same as there are certain provisions in various Acts which can be invoked when government officer does not perform his/her duty.