Normally when you view nodes in the Outliner, nodes encapsulated by a container appear twice, once at the root level and again under its respective container node. You can simplify this display by adjusting the Container Contents option. With this option you can choose to display the node only under the container encapsulating it or only under its parent in the hierarchy.
To show or hide container contents
For an even more streamlined Outliner view, you can also choose to hide encapsulated nodes altogether. This can be useful to promote the use of a container’s published attributes.