# 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