who composed the original story of mahabharata in oral form
Mahabharata Traditionally, the authorship of the Mahābhārata is attributed to Vyāsa. There have been many attempts to unravel its historical growth and compositional layers. The oldest preserved parts of the text are thought to be not much older than around 400 BCE, though the origins of the epic probably fall between the 8th and 9th centuries BCE.[2] The text probably reached its final form by the early Gupta period (c. 4th century CE).[3] The title may be translated as "the great tale of the Bhārata dynasty". According to the Mahābhārata itself, the tale is extended from a shorter version of 24,000 verses called simply Bhārata.[4]
Bhishma Parva This book of Mahabharata includes the widely studied Bhagavad gita, sometimes referred to as Gita, or The Song of the Lord, or The Celestial Song. Bhagavadgita chapters describe Arjuna's questioning the purpose of war, ultimate effects of violence and the meaning of life.[7][8] Arjuna's doubts and metaphysical questions are answered by Krishna.[9] Other treatises in Bhishma parva include the Just war theory in ancient India,[10] as well as strategies of war and troop deployment.This book describes the deaths of Uttarā kumarā (brother-in-law of Abhimanyu and brother of Uttara wife of Abhimanyu), Vrishasena (Elder son of Karna) and also Bhishma's fall respectively on 1st, 3rd and 10th days of the war. Karna didn't fought in these first ten days on Bhishma's order.