avl-tree-enter is a compiled Lisp function in `
(avl-tree-enter TREE DATA &optional UPDATEFUN)
Insert DATA into the AVL tree TREE.
If an element that matches DATA (according to the tree's
comparison function, see `avl-tree-create') already exists in
TREE, it will be replaced by DATA by default.
If UPDATEFUN is supplied and an element matching DATA already
exists in TREE, UPDATEFUN is called with two arguments: DATA, and
the matching element. Its return value replaces the existing
element. This value *must* itself match DATA (and hence the
pre-existing data), or an error will occur.
Returns the new data.