allout-structure-added-hook is a variable defined in `allout.el'.
Its value is

Abnormal hook run after adding items to an Allout outline.
Functions on the hook should take two arguments:

- NEW-START -- integer indicating position of start of the first new item.
- NEW-END -- integer indicating position of end of the last new item.

This hook might be invoked multiple times by a single command.

You can customize this variable.