So… this is what the Tree of Harmony’s avatar looks in my universe; a Kirin. Not particularly majestic?… Well, I was inspired by their (plural they pronouns, we/us/ourselves when speaking now) appearance in ‘What Lies Beneath’ and how they clearly have NO CLUE how to pilot a mortal body; not properly blinking or contracting their pupils, nor emoting properly at all.  
Their colors come from the Castle of Harmony rather than the Tree, as it offered more color choices.  
If you’re wondering why I didn’t chose to use the traditional fanart version of the Tree of Harmony… well, for one, this is easier for me to draw, and also they’re a bit more… murdery than the serene graceful deerlike portrayal than I would go with.  
See; now that we know the Tree is sapient, it means that it consciously chose to murder the Mean 6 for coming near it, and almost murdered the Young Six for not being harmonious enough. My interpretation of Harmony is heavily influenced by the fanfic ‘Hard Reset’ (Though not the sequels), and specifically this line;  
“Wow. I didn’t know what the Elements would do, but I hadn’t been expecting that. That’s actually kind of dubious, morally speaking. Forced permanent magical transformation isn’t exactly smiled upon under most circumstances. Still, if the alternative was genocide… Just another reminder that there’s a very good reason they aren’t called the Elements of Niceness.”
 
My interpretation of Harmony is essentially ‘will do anything to preserve harmony, and has no mortal nuances’. Nothing about the abilities of the conscripted to complete the tasks, only the improvement of Harmony within the group or within the world. Everything is bodies thrown and crashing against the rocks to change the world slowly, without thought to the survival of anything but Harmony.  
After all, Harmony is not good, just a state of being in peace with everything.