Hi Bushman,
I hope you don’t mind me adding to the distinguishing features. Whip Snakes and Common Tree Snakes have very similar proportions in that they are very long in comparison to thickness of their body. However, they differ in a few aspects. The head of whip snakes is almost round in cross-section (just slightly flattened) and width wise it is indistinct from the body. CTS have a noticeably dorsoventrally flattened head which is wider than the neck of the snake.
The other readily identifiable difference in body proportion is the length of the tail. Whip Snakes have fairly typical length to their tail while CTS have a tail that is two to three times that length. So CTS have a long thin slowly tapering tail while Whip Snakes have a significantly shorter tail which tapers more quickly.
Colour wise, Whip Snakes vary from brown to russet to grey, or combinations of. Two or three species can be black. All whips have a whitish belly. CTS can be green with a bright yellow belly, blue with a bluish-white belly, golden with a yellow belly or, the sometimes confusing one, black dorsally with a white belly. Whip Snakes to not climb trees or shrubs. CTS can be found on the ground but they will quickly ascend any available shrub or tree if threatened.
The white ventrals on the black form of the CTS stand out significantly more so than the white ventrals on a black coloured whip.
With minimal experience they are dead to distinguish in the field.
Cheers and I hope that helps,
Blue