Debuff debuff debuff shouldn't be the mantra, but it certainly makes things easier.
Any team over the size of 6 is a definite "no." 4-6 is the ideal team size for the trial, cause anything after that the vine spawn just becomes ridiculous. Running from memory, which mine would be considered "dodgy" at the best of times, I think at 6 members the vine spawn is 30-40, I think 24 at 4 team members... and 92 or 96 with 8. [censored] would be a good term to describe that. Almost triple with just the addition of 2 members.
Another easy way to go about this, say for example your in a team of 4. 2 level 24's, 2 level... oh we'll say in their 30's. BEFORE you get the trial, Malefactor to the lowest levels you can. BEFORE you even talk to Sparcetrile (or however it's spelled.) In our example, the 2 level 24's would mal the 30's down to 24's. Also, make sure everyone is set to "Villainous" as their difficulty. Most likely only the leader it matters, but hey... we want to be sure.
Got your mission? Good... un-mal and go kill them pesky CoT. Done? Mal down again, get your next mission... stay malefactored and enter the mission. Once everyone is in, un-mal and lackey up. So, going by our example again, the 24's would Lackey up to the 30's. Do the mission, should be quite easy...
Wash, rinse, repeat for each mission.
There are easier ways to do this, but I won't get into it here as it involves logging off and a TPing stalker (or someone with powers equiv to hide.)
Now the end, hopefully all the baddies should be well below your current lackeyed levels and HOPEFULLY, the tree shouldn't be able to one shot anyone. Run the circuit around the tree, killing all the CoT you see, then run the circuit again killing vines. Should be straight forward after that.
Hope this helps!