Add multi-level taxonomy term selection field with multiple selection for last level I want to add field with taxonomy term selection
If suppose I have vocabulary as Food and it has hierarchy of terms like below: 

Fruit
- Mango
- Apple
- Banana
Vegetables
- Spinach
- Potato
- Tomato


While selecting taxonomy terms in a node I want to first select Fruit or Vegetables and after that another select list should appear with provision to select multiple sub terms for respective top level terms

Example: If I select Fruit from first select list only single selection allowed and then second select list should appear with Mango, Apple, Banana so one should have chance to select multiple fruits from second select list

I tried simple hierarchical select but it doesn't give provision to select multiple terms on last level field.
Have a look at Taxonomy Term Reference Tree Widget module. This does exactly what you need as per its documentation.

Edit: Since now I bettter understand your requirement, you might want to try Hierarchical Select.