What is the design of the 'menus' table? What is your primary key? Because the error is that you don't give it a value, and there is already a record in place with value 0 (probably from your first save).
As with all ORM models, every table needs a primary key, even if it's not used anywhere. If you don't define one, it's supposed to be 'id'. So it's either not present, or not defined as auto-increment.
I am creating a Controller_Install for doing Migrations and Basic Menu generation, in Controller_install i will create action_menu(), so that which do Menu Generation while calling, also action_migration(), which do migration while calling, Am i Currect?
2ND Q/
IN FUTURE, CAN I MAKE CHILD MENU BETWEEN TWO MENU AFTER GENERATING COMPLETE MENU?
That's very application specific, I can't comment on that.
With your second question, you mean add a submenu to an existing menu structure? Yes, the NestedSet model contains all the methods for tree manipulation, including adding nodes or other tree structures, move nodes around, etc.