Final answer:
The immediate action when new content is missing from the Content Library Tree is to close and re-open the Content Library Tree. This action helps to refresh the interface and display new items.
Step-by-step explanation:
When new content is missing from the Content Library Tree after saving it, the immediate action should generally be to close and re-open the Content Library Tree. This can resolve issues where the interface has not updated to show new items. However, if this does not work, the next steps could include checking for any errors during the save process, ensuring the content was saved to the correct location, and verifying that user permissions are correctly set to see the content. Depending on the system or platform you're using, additional actions such as refreshing dynamic sources or deploying configurations might be necessary, but starting with the simplest solution is often effective.