Provide an API for inserting and returning raw BSON

In my code I catch the exception bson.errors.InvalidDocument to check if my document is too large. If it is I need to split the document to smaller documents. To check the size of the resulting documents I go ahead generate the BSON object. It would be nice to be able to pass the BSON object to the insert the method instead of having insert do the BSON conversion again.