I purchased a young river birch over the weekend (not yet delivered) with the intent of planting it within a raised area behind a retaining wall (not yet built) less than 24" above normal grade. The retaining wall is simply to provide level ground to the adjacent area (area to left in pic). All of this would be placed on the corner of my home extending roughly 12-13' from the corner measured diagonally.

My first question is whether or not the retaining wall around the birch is a bad idea. Would the roots destroy the wall? Or is 2' shallow enough for the roots to develop underneath.

The next question would be how large of a wall should I build around it. My initial layout looked good at roughly a 6' radius centered on the tree location. But my worries of crowding it set in quickly.

My home is fairly new build so I do have the flexibility of changing planting plans or layouts

Any feedback would be much appreciated!