Chandogya Upanishad
This Upanishad is part of Chandogya Brahmana of the Sama Veda which is one of the largest important Upanishads with 8 chapters (Prapathakas) with many verses including some stories as themes to gain Upanishadic knowledge. The first 5 chapters forms the part of Karma Kanda and Upasana Kanda and the remaining 3 chapters form the part of Jnana Kanda.
This Upanishad is placed in the 9th position in the list of Ten Principal Upanishads. The name of the Upanishad is derived from the word “Chanda” (Rhythm~ poetic meter). This Upanishad directly deals with the true nature of Brahman, the Supreme Self, without a second.