I am using drupal 7 and book module. On node add/edit form for book content type when adding new book page there is Book outline tab at the bottom, When you select Book from first Select field, a second Select field appears called “Parent item”. I want to change this SECOND Select field into tree format, So that it lists down only parents and when clicking on one of parent it will further list down its children and so on instead of having one Select field and keep the the functionality same.
I have searched and tried for many contributed modules, but none of them solved my problem so far. Please help me in this regard, I would like to know the better approach to achieve this goal. Also, please tell me is there any module available for this or the only way is to write a custom module? in case of custom module which hooks can be helpful.