Cesium.CesiumTerrainProvider / GeoserverTerrainProvider

I have a question.
I would like to upload elevation data as source.
Please tell me how to upload using API ‘Cesium.CesiumTerrainProvider / CesiumTerrainProvider’.
Or let me know if there is another way.
But please tell me how to do it without the use of cesium ions.

You can try tum-gis/cesium-terrain-builder-docker and geo-data/cesium-terrain-server on github. It works for me when I tried some local, small-scale terrain data.