This diagram illustrates a tree structure for categorizing animals.

At the top is the root node, with one child node named "Animals". Below that are child nodes named "Fish" and "Mammals". Below the "Mammals" node are child nodes named "Dogs" and "Cats". Below the "Dogs" node are child nodes named "Collies", "Greyhounds", and "Beagles". At the lowest level, below the "Collies" node are child nodes named "Fido" and "Spot", and below the "Beagles" node are child nodes named "Fido" and "Ginger".