All of us are aware of the Yoga system of Patanjali through his work Yoga Sutras ans he is regarded as the founder of the Yoga system of Indian Philosophy.
We also have Shiva sutras which deal pretty much on the same subject.
We have yet another treatise on Yoga in the form of a minor Upanishad, Yoga Kundlini Upanishad.
This Upanishad is from the Krishna Yajur Veda.
It has three distinct approaches o the Yoga.
It deals with Chitta primarily.
Patanjali describes what Yoga is in his first sutra,
‘Yoga: Chitaa Vrutti Nirodha’
Cessation of the modification of Chitta is Yoga.
Elaborating on this sutra , the Yoga Kundalini Upanishad discusses the different methods, some are different from Patanjali’s.
It deals with an exposition of Hatha and Lambika Yogas.
It concludes with an account of the non-qualified Brahman,that is the Nirguna Brahman.
Patanjali found it necessary to have a Personal God, Ishwara for practicing Yoga.
The Non-dual Brahman is , in the opinion of Patanjali, is easier to realize through the Personal God,Ishwara.
Please read my posts on this.
Kundalini Yoga analyses the nature of Chitta in deatil
It maintains that Samskaras and Vasana( remnants of actions performed ,( both now and in the past births) and Prana, the Vital Breath constitute the
causes for the existence of Chitta.