Over time, the more common mistakes would be integrated into the tree. If some people feel indigestion as a headache, then there will be a probability that "headache" is caused by "indigestion" and questions to try to get the user to differentiate between the two.

And it would be a supplement to doctors rather than a replacement. Early questions could be handled by the users themselves, but at some point a nurse or doctor will take over and just use it as a diagnosis helper.