index (SNMP::ObjectId)

    # 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