Heaven Tree is a Webring.
A webring is an alliance of sites which link to their "neighbors" in a circular way. Each site places "Next site" and "Previous site" links which, if a user continues to follow, he will see every site in the ring and end up where he started.
This is a classic way to discover artisanal sites on the Internet without the mediation of search engines, "big tech" or corporate landing pages.
Don't surf too long!