func (c *MergeCache) Put(id int64, tree io.Reader) (retErr error) {
	return c.Cache.Put(fmt.Sprint(id), tree)
}
func (c *MergeCache) Put(id int64, tree io.Reader) (retErr error) {
	return c.Cache.Put(fmt.Sprint(id), tree)
}
// Put puts an id/hashtree pair in the cache and reads the hashtree from the passed in io.Reader.