In the ancient world the tree is not worshipped for itself only, but because it manifests the workings of a wholly other sacred power or force, which is both feared and venerated. This power reveals itself at the cosmic center and radiates throughout the whole. "As a living embodiment of both the centre and the whole, the sacred tree becomes the Cosmic Tree, which by its natural laws of development (its annual 'death' and 'rebirth') embodies the perpetual regeneration of the Cosmos from the Source."
The Assyrian king appears twice, raises his right hand and points his right index finger in a gesture of worship toward a god in a winged disc. He holds a mace, the symbol of authority. The Sacred Tree (which is probably a palm tree) lies in the middle of the relief. The relief was originally positioned behind the king's throne.
Image: King Ashurnasirpal II and a winged god worshipping the sacred tree, alabaster relief from Nimrud, Neo-Assyrian, 9th C. BC.
Quote and image from The Tree of Life: Image for the Cosmos, by Roger Cook.