ADirStat is a treemap visualisation for your android storage usage. It shows a similar view to KDirStat (Linux) and WinDirStat (Windows).
Large files and directories can easily identified, even if they are deep in subdirectories. Unneeded files can be quickly deleted or inspected further.
ADirStat can be found on the play store: https://play.google.com/store/apps/details?id=org.flightofstairs.ADirStat
ADirStat uses icons from https://github.com/google/material-design-icons