Treeman looks veiny. Alright, some abilities? He's broken but pulled himself together. Inspiring! But not without some baggage. I see him as a mobile sort, maybe support.
Traumatic Pulse: Treeman blasts out an expanding wave that gains more power the more damage it absorbs. AoE mine after set time. Upon second activation he gets sucked into the center and launched like a bullet whichever direction the ability was first activated towards. Planning! Procs explosive damage.
Superfluous Twin: Treeman can teleport to any friend or foe. Allies he can simply look at their name and he branches out and floats alongside them like a second sentinel indefinitely. Especially useful on fallen allies where he can appear instantly to help them. Co-op! Their pace is yours. Enemies he must tag them first. If they die, it can create a warp point for more flexible teleporting.
Downward spiral: Enemies spiked with this affliction create a miasma in their wake. The more enemies attracted to the center, the more poisonous it becomes. When used in conjunction with Superfluous Twin it becomes an explosive bolt. Pinning the live target to a surface before detonating.
Recursive Vacuum: Treeman breaks physics. Two points are assigned and then the surfaces becomes portals to one another both pulling and pushing enemies away. The closer the two points are, the stronger the results are. Along with any associating ragdoll physics. One can't work without the other though. If enemies are spiked into an opening using Downward spiral it creates a shockwave.
Passive. Focus tree passives are yours too.
Some rough ideas but there you go.