avl-tree-member is a compiled Lisp function in `avl-tree.el'.

(avl-tree-member TREE DATA &optional NILFLAG)

Return the element in the AVL tree TREE which matches DATA.
Matching uses the comparison function previously specified in
`avl-tree-create' when TREE was created.

If there is no such element in the tree, nil is
returned. Optional argument NILFLAG specifies a value to return
instead of nil in this case. This allows non-existent elements to
be distinguished from a null element. (See also
`avl-tree-member-p', which does this for you.)