No trees in the stdlib?

[Tom Reed]

Why no trees in the standard library, if not as a built in? I searched 
the archive but couldn't find a relevant discussion. Seems like a 
glaring omission considering the batteries included philosophy, 
particularly balanced binary search trees. No interest, no good 
implementations, something other reason? Seems like a good fit for the 
collections module. Can anyone shed some light?

Thanks.
--
Tom