Please see my comment to the question. In simplest case, if you have some graph (not only a tree) with the
nodes of the same type, it can be represented by a single table, a table of nodes. Each record should have one or more
attribute used to indicate
relation with other node pointing to it by its
primary key. (For AVL, such attributes could be
left
and
right
.) Such relations represent graph
edges.
Please see:
http://en.wikipedia.org/wiki/Relational_model[
^],
http://en.wikipedia.org/wiki/AVL_tree[
^],
http://en.wikipedia.org/wiki/Graph[
^].
—SA