Theres a picture in Matheney & Clarke of a tree located on a creek-bank, captioned along the lines indicating the rooting pattern of the tree will typically have
“large tree roots (oriented) to run parallel to the banks and (be) quite shallow". (Ref: Matheney N.B., ‘Trees & Development: A Technical Guide…” 1998).
The theoretical symmetric root-plate scenario of a tree is such a location, therefore, would be unlikely.
Here some pics showing whats really going on.
Base 10.jpg Tree 12.jpg Base 11.jpg T6.jpg View 11, 12.jpg