Wordpress Category to Menu

I have created several categories with sub-categories, I want to display the category in a menu so I created the menu inside appearance-->Menus, now what I want to be displaying is the created categories(with the respective sub-categories) in the menu. I went to the categoryName, when I selected the Category1 with the hope of getting all the sub-categories automatically, I only get the Category1 back, when I clicked view all-->select all-->add to menu unfortunately it shows all the categories with the sub-category at the same level. Please how can WordPress newbie, that have close to zero knowledge of php programming achieve this task? Or is there any plugin for that?