Rincewind, whilst escaping mad bears, swarming bees, and a pack of wolves trying to get away from the former and enraged by the stings of the latter, climbed her tree for sanctuary. Alas, a branch gave way and he found himself plummeting downwards, whilst the branch didn't break cleanly: it tore a strip of bark and living tissue away with it. It was at this point that an arm emerged from nowhere - well, out of the otherwise solid bark - and drew him into the tree.
This was Druellae with, as Rincewind noticed, a nasty fresh scratch on her arm, which was the result of the damage he had done to the tree. She had drawn him into the palatial interior of the living tree, which, Tardis-like, was far bigger on the inside than the outside, and populated mainly by female dryads: beautiful, naked, and in various shades of green.
This distracted Rincewind's attention for long enough for him not to notice the male Dryads - very obviously male, for e.g. in details of strength and musculature. Who were standing behind him blocking his exit.