# File lib/snmp/varbind.rb, line 207
    def index(parent_tree)
      parent_tree = make_object_id(parent_tree)
      if not subtree_of?(parent_tree)
        raise ArgumentError, "#{self.to_s} not a subtree of #{parent_tree.to_s}"
      elsif self.length == parent_tree.length
        raise ArgumentError, "OIDs are the same"
      else
        ObjectId.new(self[parent_tree.length..-1])
      end
    end