ext_tables.sql

Please add the line from below to your table definition in your ext_tables.sql

CREATE TABLE my_table (
  ...
  rootpid int(11) DEFAULT '0' NOT NULL,
  ...
);

Replace "my_table" with the name of your table.

You may use another field name than "rootpid" for example "my_rootpid". But then you have this to configure in your TCA too. See the ctrl section in the TCA