This bundle was refactored into the TreeBrowserBundle and the old bundle removed after a while. See here for the discussion about that: https://groups.google.com/forum/?fromgroups=#!searchin/symfony-cmf-devs/treebundle/symfony-cmf-devs/k7nm-XtXW8Q/kgZpaOJN1x8J
If you can update your project, then just do that and drop the reference to TreeBundle. Otherwise the easiest would indeed be to include it in your own repository.
We assumed that the early adopters of the CMF frequently update, and thus we removed this repository after a few months. Sorry about that. We will be more careful with backwards compatibility the more stable we get.