Trunks come in a wide range of shapes and configurations.
My guess is that
@fredman is correct and this one just has 2 strong roots that have expanded the trunk more just above the roots. I have also seen flattened trunks where they were confined in a narrow space before collection.
An oval trunk is not necessarily a problem but it is best if the front is one of the wider sections rather than a narrow side.
You won't hurt the tree by digging gently down to find the main roots. Even if you uncover some small roots on the way they will be fine when you cover up again after.
Plan of attack will depend on what you find but I suspect a layer to create new roots will be the best course.
There are several ways to tackle the upper trunk.
You can cut the top on an angle then grow a new leader out to get a larger tree with good taper. That will take some years.
You can hollow out the trunk to look like an old trunk that has rotted out on one side. That can look impressive and is quicker but first attempts do not always look completely natural.