How to import listing with sub category ?

How to import listings with subcategory assigned to theme. If I assign a subcategory in the csv sheet, the which already exist in my site, then instead of assigning the listing to that sub-category, it create a new category in that name.

e.g. I have a category, Physics and a sub-category, Bio-physics in my site.

Now, I want to add a listing in the subcategory, Bio-physics, so I write Bio-physics in the csv file, category column. After Import, the listing is supposed to be in the sub-category, Bio-physics.

But, here, a Category has been created with name, Bio-physics and the listing has been assigned to that category.

Any help ?