We have a Mt Fuji, Prunus 'Shirotae', tree with a total diameter of about 8 meters (26 feet). We only have a small garden but love this tree. It's planted next to a brick retaining wall (goes down to our driveway). For a long time it's been fine but it finally started pushing out the retaining wall with a large root. The trunk is about 20cm (8in) in diameter and the root must be about 10-15cm (4-6in), so it's a major one. I'm sort of okay to just leave it and let nature take its course but an alternative would be to slice out the outer part of the root which is against the retaining wall. How bad would this be for the tree?
Overview of area:
Looking in more detail, I now see that the tree itself is probably pushing a bit now on the retaining wall. I think the only solution is to actually remove the retaining wall and perhaps rebuild it to suit the tree. Suggestions?