Sorry, but unless you build it in such a way that there is no soil touching the trunk of the tree, then you will cause stem rot and the tree will eventually die.

Thankyou Owdboggy, I guessed as much but now I know for certain, it's back to the drawing board.

You can quite easily put a sleeve round the trunk of the tree to keep the soil off but my concern would be the roots of the tree invading the compost in the raised bed, making it difficult to work.

Not to mention that Cherries loathe root disturbance, and a lot of their roots are pretty close to the surface.

Thanks Bulbaholic and Bamboo, the idea of the protective sleeve around the trunk was quite appealling but the root disturbance issue would put that out of the running. The existing bed, with tree in the middle, has a 2ft wall around 3 sides between 2 drive entrances and I wanted to build up the 4th side. Obviously that would mean digging foundations for the wall, which would only be 2ft from the trunk. Not a good idea me thinks.

A sleeve wouldn't help unless it was rigid enough to keep the soil at least 15 cm from the trunk.