Pheromosa @ Focus Sash  
Ability: Beast Boost  
Level: 50  
EVs: 252 Atk / 4 SpA / 252 Spe  
Naughty Nature  
IVs: 0 Def / 0 SpD  
- Low Kick  
- Lunge  
- Ice Beam  
- Protect 
Pheromosa baits a great number of attacks with its paper thin bulk and 0 defensive IVs, though not as many as you would hope due to the Tree's improved AI.  It is *extremely* good at baiting once it's down to its Focus Sash.  Fighting/Ice has good coverage while Bug puts big damage into most (Psychic-type) TR setters so the team doesn't take a huge deficit on Turn 1 by going into twisted dimensions.

Tapu Lele @ Psychium Z  
Ability: Psychic Surge  
Level: 50  
EVs: 252 HP / 180 Def / 4 SpA / 4 SpD / 68 Spe  
Modest Nature  
IVs: 0 Atk  
- Psychic  
- Moonblast  
- Taunt  
- Protect  
Tapu Lele is the bulky nuke for the team.  Terrain-boosted Shattered Psyche KOs almost every single Pokemon in the tree which doesn't resist it, with the exceptions being super bulky things like Blissey and Suicune and flat out dumb sets like Darmanitan-3.  Anyway, Lele is great; takes most hits like a champ and puts big damage into things. I'm honestly not really sure how to describe its role on the team or how it functions because apparently after 195 games even the team's original creator, Level 51 on Smogon and the Battle Facilities Discord server, is still not exactly sure. Oh well.

Salamence-Mega @ Salamencite  
Ability: Intimidate  
Level: 50  
EVs: 4 HP / 252 Atk / 4 Def / 12 SpD / 236 Spe  
Jolly Nature  
- Double-Edge  
- Earthquake  
- Flamethrower  
- Protect  
Pretty standard set.  Double-Edge for strong STAB.  Earthquake for coverage and works well with allied Protects/King's Shield.  Flamethrower is still run even with a Jolly nature to hit 4x weak mons without reducing bulk.  The Speed EVs hit a Speed stat of 187, which speed ties with Hawlucha-1 and Hawlucha-4, neither of which pose a significant threat to my team, while still outrunning Salazzle-1, Salazzle-2 and Salazzle-3 (185 Speed stat), which threaten both my leads with super-effective hits. I'd have used a Speed stat of 186 but you literally can't hit that thanks to how Natures work. The rest of the EVs are dumped into bulk for a minor increase in bulk—but in the Tree, any bulk is good bulk.

Aegislash @ Leftovers  
Ability: Stance Change  
Level: 50  
EVs: 252 HP / 220 SpA / 36 SpD  
Quiet Nature  
IVs: 0 Atk / 0 Spe
- Shadow Ball  
- Flash Cannon  
- Wide Guard  
- King's Shield 
Wide Guard is really nice for this team, since it helps to patch my matchup against Ground-types (essentially just Earthquake) and Best Move In The Game™ Rock Slide. That's really about it. STAB Shadow Ball was also pretty nice for getting big damage onto Psychic types once Pheromosa was down, I guess. Not much to say about this Pokemon, but it does help with the team's overall bulk so it isn't a team of 4 pieces of paper defensively.  For those who don't understand Aegislash's mechanics, 0 speed IVs is to ensure that Aegislash takes hits in Shield form before attacking in its frail Sword form.