Items are arranged in a tree browse window in a hierarchical structure. In order to see items further down the structure, you may need to expand a branch of the tree. If an item in a tree browse window has other items below it in the structure, you will see a plus (+) sign next to the item.
If you single mouse click on the plus sign, the tree branch will be expanded. Alternatively, you can double click on the name of the item, and the tree branch will be expanded.