Some posts discuss on ways to hide the form directly from the interface, but the change isn't seen from the other players.
When one player make the choice to hide it.
I think it was a good move from blizzard to give us the choice to heal in tree form or not after cataclysm.
Here is my suggestion to implement it on Warmane :
Either in the form of a Special Glyph, purchasable in the store with coins - Glyph of the Tree of Life
( Hides the Tree of life Form and the Spell will now be displayed as a Buff or an Aura )
Either in the form of a Scroll, purchasable in the store with coins - Scroll of the Tree of Life
( Activate - Deactivate the Tree of Life form to be displayed while keeping it as a Buff or an Aura while healing )
Even beyond the impact something like this could have on PvP, this sort of custom change just isn't something we do. It would be a bad precedent to do it for something this irrelevant too. You already have the means to model edit that for yourself if it bothers you that much, and don't really have any right to impose that on others who want to visually identify when you're capable of healing or not.