--- a/mercurial/exchange.py	Wed Jan 06 20:05:18 2016 +0000
+++ b/mercurial/exchange.py	Fri Jan 08 21:13:06 2016 -0800
@@ -1519,6 +1519,8 @@
         if version is not None:
             part.addparam('version', version)
         part.addparam('nbchanges', str(len(outgoing.missing)), mandatory=False)
+        if 'treemanifest' in repo.requirements:
+            part.addparam('treemanifest', '1')
 
 @getbundle2partsgenerator('listkeys')
 def _getbundlelistkeysparts(bundler, repo, source, bundlecaps=None,