code: func NewTreeIter(s storer.EncodedObjectStorer, iter storer.EncodedObjectIter) *TreeIter {
  	return &TreeIter{iter, s}
  }
docs: // NewTreeIter takes a storer.EncodedObjectStorer and a
  // storer.EncodedObjectIter and returns a *TreeIter that iterates over all
  // tree contained in the storer.EncodedObjectIter.
  //
  // Any non-tree object returned by the storer.EncodedObjectIter is skipped.