Version 3.18 is available upstream. Please consider updating!
It seems that version 3.18 is available upstream, while the latest version in the Gentoo tree is 3.17. You think this warning is false? Read more about it here.
The tree.hh library for C++ provides an STL-like container class for
n-ary trees, templated over the data stored at the nodes. Various
types of iterators are provided (post-order, pre-order, and
others). Where possible the access methods are compatible with the
STL or alternative algorithms are available.