How to place every node of a content type under a menu item?
You can use Default Menu Link module for this and core menu settings for content type..


  Provides the user with a check box on all content types to set the
  "provide a menu link" value to true by default.
  
  This is basically a nice way to ensure the menu system is adhered to
  by all content authors.


You need to set Menu settings for content type..