Go to the Drive audit and under Shared (Team) Drive, select the root folder you want.
Click on the drop-down menu beside the folder name and select Show contents of this folder and sub-folders.
This will expand the entire folder tree and take you back to the Files tab for this search.
In the Files tab, click on the link Show stats for the current filter.
This will give you a complete breakdown not only of the Shared Drive folder trees, showing the number of folders and files, but it will also show you the file types.
Clicking on any file type in this table will pull back just those files that are of that type from the tree.