I have read several times that Vyasa only wrote from Bhishma Parva to Ashvamedhika Parva, while Vaishampayana extended the work by adding Adi Parva, Sabha Parva, Vana Parva, Virata Parva, etc. Is this true?
The Rishi Vyasa published this mass of knowledge in both a detailed and an abridged form.
This is furthee explained as below:
Vyasa executed the compilation of the Bharata, exclusive of the episodes originally in twenty-four thousand verses; and so much only is called by the learned as the Bharata.
Afterwards, he composed an epitome in one hundred and fifty verses, consisting of the introduction with the chapter of contents. This he first taught to his son Suka; and afterwards he gave it to others of his disciples who were possessed of the same qualifications.
After that he executed another compilation, consisting of six hundred thousand verses.
thirty hundred thousand are known in the world of the Devas;
fifteen hundred thousand in the world of the Pitris;
fourteen hundred thousand among the Gandharvas, and
one hundred thousand in the regions of mankind.
Narada recited them to the Devas, Devala to the Pitris, and Suka published them to the Gandharvas, Yakshas, and Rakshasas: and in this world they were recited by Vaisampayana, one of the disciples of Vyasa, a man of just principles and the first among all those acquainted with the Vedas. Know that I, Sauti, have also repeated one hundred thousand verses.
So it seems, the complete Maharashtra was composed by Vyasa along with abridged version.
This work is a tree, of which the chapter of contents is the seed; the divisions called Pauloma and Astika are the root; the part called Sambhava is the trunk; the books called Sabha and Aranya are the roosting perches; the books called Arani is the knitting knots; the books called Virata and Udyoga the pith; the book named Bhishma, the main branch; the book called Drona, the leaves; the book called Karna, the fair flowers; the book named Salya, their sweet smell; the books entitled Stri and Aishika, the refreshing shade; the book called Santi, the mighty fruit; the book called Aswamedha, the immortal sap; the denominated Asramavasika, the spot where it groweth; and the book called Mausala, is an epitome of the Vedas and held in great respect by the virtuous Brahmanas.