It's possible to get the direct children of the folder with the https://www.googleapis.com/drive/v3/files endpoint. Example:

https://www.googleapis.com/drive/v3/files?q='folderId' in parents

You wont be able, however, to get the whole tree from this, you would need to query the contents of the subfolders on demand.

Source: https://developers.google.com/drive/api/guides/search-files

Source: https://developers.google.com/drive/api/guides/ref-search-terms#file-properties