[Zope] BTreeFolder2 add speed with 10k objects

I'm using a CMFBTreeFolder to hold objects for a query later. Each object in the folder has a few string members. The folder now has about 10,200 objects. When I add a new instance of the object to the folder, it takes around 18 seconds. I've tracked the hotspot down to BTreeFolder2._setOb()'s: tree[id] = object which takes around 17 seconds. By comparison, the rest of the request including cataloging the object takes less than a second. I'm using Zope 2.6.1, CMF 1.3.1. I updated by BTreeFolder2 code to the latest from CVS and ran manage_cleanup() which reported no errors. Any ideas how I can improve this? Thanks, Jeff