First, set up the animation as you would for a regular bulleted list. Under "Effect Options", select "By Paragraph". At this point, you'll get each main bullet separately, but the sub-bullets come all at once with their parent.
Now, click the button for "Animation Pane" to open a set of more detailed controls. On the right side of the screen you'll see a list of all the bullets (paragraphs) in your slide.
The numbers in that list correspond to the order they will appear in. You will note that there's a number next to each of the main bullets, but not the sub-bullets. That means the sub-bullets lack their own animations and will be included in the main ones.
Right-click on one of the sub-bullets, and select "Start On Click." That will separate it into its own animation. You can tell it worked because it will now have its own number in the list. Now on the slide show, it won't show up with the prior main bullet, and will require an additional click for itself.
You can do this for all bullets and sub-bullets at once. Click somewhere in the slide, push Ctrl+A to select the whole slide, and then right-click one of them in the animation pane to change the setting for all.