Size of raised bed for Semi-Dwarf Cherry Tree

Hi everyone,

I just bought a Summer Sun on Gisela rootstock from ChrisBowers website

I plan on building a square raised bed in sunny corner of our garden but I am unsure what size to make the square raised bed. This is the first time I am planting a tree ever and i have bought a stake and irrigation kit.

I have a small garden so intend on pruning to keep it small and narrow (2 meters perhaps). Not sure yet how to prune but I am hoping the information that comes with the tree will help

Thanks
Sasha