In Egyptian mythology, Saosis was a goddess, known principally for her acaciatree, located north of Heliopolis. Many of the gods, and most especially Horus, emerged from her tree.
Strictly, the myth states that Atum ejaculated his Semen into his mouth, impregnating himself, possibly indicating autofellatio, which has lead many to misinterpret (euphemistically) the myth as indicating creation from mucus).
Later belief held that Shu and Tefnut were created by Atum having sex with his shadow, which was referred to as Iusaaset (also spelt Juesaes, Ausaas, Iusas, and Jusas, and in Greek as Saosis), meaning (the) great (one who) comes forth.
Consequently, Iusaaset was seen as the mother and grandmother of the gods.
In Egyptian mythology, in the Ennead system of Heliopolis, the first couple, apart from Shu and Tefnut (moisture and dryness) and Geb and Nuit (earth and sky), are Isis and Osiris.
They were said to have emerged from the acaciatree of Saosis, which the Egyptians considered the tree of life, referring to it as the tree in which life and death are enclosed.
A much later myth relates how Set killed Osiris, putting him in a coffin, and throwing it into the Nile, the coffin becoming embedded in the base of a tamarisk tree.