With the cure and magic stone in hand, I returned to where the others were exactly the way I got separated from them. After asking the tree about our whereabouts, it seems that I've left my body and gone into a world between time and space, a world created by the tree itself. It is a place where we're closest to the tree's soul, closest to the tree's magic core. It is the only place where we can listen to and talk to the tree, and it's only open to those who know.
The tree sensed the people's distress as they came here and would open its door based on how dire their situation and needs were. It was done to ensure that the tree could help people who were actually in need, rather than those who were bored with life or simply on one of their made-up missions.