I think the tree trunk and the main center portion of our tree is our most likely path. We place lessons along the way for ourselves. But at any moment, we could veer off onto a branch. Some branches are wide, others are tiny and narrow (but can be very rewarding). Some branches cross over others, allowing us further choices, and some branches have dead ends (literally).
And then there are times when a soul has so exceeded it's own expectations for that lifetime that a new path is negotiated by the higher self even while the person is in a body already.
I do not feel that this interferes with free will at all. We can make any choice at any time, and also we are the ones who made any choices that seemed pre-destined (like who our parents are).