What are the differences between the CPI and CPI(M) in India?

Communist Party of India (Marxist) and Communist Party of India (CPI) were both the same before the 1960s. There was only one party which was   Communist Part of India (CPI). Around the 1960s, there was  a conflict between two groups within the party regarding the  ideological direction of the Class conflict . India under the leadership of Pandit Jawaharlal Nehru was trying to follow Soviet's socialist feat but from the mirror of Congress-ideology.  A fraction of the then CPI party didn't believe that Congress was  trying to follow Communism and also believed that people of the Congress  party were class-enemies, hence, it was of no use to support them.  Another fraction of the CPI party believed that as Congress is trying  make partnership with Soviet, they might give temporary support to the  Congress government in their work. There was tension regarding this  decision. At the same time, Communist Party of China was not liking Soviet's way of ruling. During Sino-Indian War , the division between the two fractions of CPI party got widened. One fraction believed that this was a war between a capitalist state and a communist state; other fraction believed on a strategic tie with the government. Two of those fractions between the party also got divided based on the ideological division of Soviet's and Chinese Communist parties.  The section which supported Chinese direction got separated from the  CPI and formed a new party which is now called Communist Party of India  (CPIM).

CPIM got their symbol as :

CPI got their symbol as :

After the split, there are several tries made to merge those two parties. The core essential classification of the society of the two  parties are not much different.
 Since, the partition of the parties, CPIM only increased their power, while CPI lost it gradually. However, they both have their own follower-base. Their analysis is that if they try to merge, then they might loss their own follower-base significantly. So, they have resisted the merging. In my opinion, instead of merging the parties under one name, it is essential that all the core-leftist parties have their own understanding solid and have a unification based on the basic common ideology. There are parties like Socialist Unity Centre of India (Communist) , Communist Party of India (Marxist-Leninist) Liberation and others which are not in the leftist-coalition. Some parties like Revolutionary Socialist Party (India) is having their internal fragmentation. If all of those parties can come to a common platform to agree to some common issues for a greater leftist-coalition and fight against the common capitalistic propaganda, then that would be a fruitful progress in expanding leftism in India.