As you move from an animal's class to its order, it becomes part of a group that is closely related

As you move from an animal's class to its order, it becomes part of a smaller group that is more closely related.

Explanation:

There are seven levels of classification for animals. The highest level of classification is Kingdom which is Animalia that include all the animals present on earth.

So the seven-level of classification are Kingdom, Phylum, Class, Order, Family, Genus, and  Species. When we move down in the classification level the similarities increases between animals and when we move up from species to kingdom the similarities decrease between animals.

So by moving from higher-level like class to lower level like order the number of animal groups will become less and they become more closely related due to increase in the genetic similarities between them.

the answer is trees if i'm not mistaken