gdal: build from source with python bindings in docker container

I’m struggling with building a gdal feature branch from source. My environment is docker with an ubuntu base image.

It builds fine, but invoking gdal2tiles.py throws the notorious

ModuleNotFoundError: No module named 'osgeo'

These are my build steps in my docker container:

RUN cmake -DBUILD_PYTHON_BINDINGS=ON -DCMAKE_BUILD_TYPE=Release ..RUN cmake --build .RUN cmake --build . --target install

Clearly I'm missing something for being able to import osgeo in python. But what is it?