Starting from the Marbruk Wayshine, go through the arch to the south towards Bramblebreach. The quest is almost directly south of the wayshrine, just a little to the left of Bramblebreach.
Talk to the Khajiit Hazazi who is having trouble convincing the Bosmer there to join the Dominion. They are opposed to Queen Ayrenn and just want to play jokes on him and pull his tail. The Vestige offers to help, and Hazazi tells them to talk to Treethane Niriel. As soon as he mentions the Treethane, a Bosmer walks up and starts dancing behind him. The Vestige can hear Hazazi say "If only Hazazi was allowed to eat you","Enjoying the Dominion or not?" and "Why do you dance?"
Go up the root path to the Treethane's Chambers on the left. The Treethane is sitting in a wooden chair in the back center of the room. She thinks the Vestige is a tourist and mentions that they don't get many visitors, which most choosing to stay behind the shiny, new walls of Marbruk including King Camoran. Their problem with the Dominion is that the Wilderking, who they obey, doesn't seem to like Queen Ayrenn. In order to talk with the Wilderking, they need to gain the Treethane's trust by driving away the Wood Orcs, then they need to plant Lurchers in the camp, then kill the Wood Orc Chieftain.
The Shimmering Tree has the lurcher seeds. Go down the path and head east. On the ground level, the Vestige may see drummers and dancers. This path takes them past some more treehouses, those these ones are closer to the ground. The Shimmering Tree is behind two houses. It looks like a small palm tree surrounded by red flowers. Approaching the tree will cause the quest objective to change from 'Find the Shimmering Tree' to 'Talk to Aranias' who is kneeling to the left of the tree. Aranias also asked to see the Wilderking. She and a colleague offered to drive out the Wood Orcs, but the Treethane turned them down. She suggests they use essence from the Kollopi tree to hide themself in a cloud of forest moths, so the Wood Orcs won't see them. The Vestige can ask her about her background, the Wilderking and Andurs.
Andurs is standing behind her. He has been watching the Wood Orc camp. He says not to attack the entire camp and to be careful when fighting the Chieftain. He suggests attacking the shaman who is always near his side first.
The Kollopi essence and seeds are collected from the tree, and the Vestige heads off to plant them. The planting sites are inside Camp Gushnukbur, which is surrounded by a tall wooden wall. There are Senche Tigers and Orcs to fight, but once the Lurchers are planted they will help, too.
A Wood Orc shaman and lookout will be waiting near the east side of the camp. The shaman can teleport. Defeat them and enter the cave.
Inside, there are more enemies, including Ravagers, Rangers and Sentries. The Shaman and The Chieftain are sitting at a table in the south end of the cave.
Once they are defeated, go back to the Treethane. She keeps her bargain and gives the Vestige 200 gold.