Recently spent a few days at Treants myself with my shammy arriving there at 29.
I found the best approach was to nuke twice with frost strike which gets them to roughly 50% hp then I would use my poison wind censor to hit them down to roughly 41-43%. They cast heal below 40% from what I saw. So at 41-43% i stopped attacking and blasted with a final frost strike which takes them below 20% in which time they start running and then just bash them down to finish.
The key is to engage them before they buff up, this is what I did and it worked well for me give it a shot see how you get on
Elu
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