GEDCOMs are no longer directly imported into WikiTree. Instead, you are expected to compare the profiles in your GEDCOM to possible matches that already exist in WikiTree. We call this new system GEDCOMpare.
Using GEDCOMpare, if you find a match, you may be able to add any new information from your GEDCOM, depending on the privacy level, trusted list access, and/or other factors like Pre-1700 and Pre-1500 certification. If you are not restricted by the aforementioned factors, you can edit matches "on the fly."
If you don't find a match for a particular profile, you cannot add a new profile until you have processed all the profiles in your GEDCOM. Once your GEDCOM has been completely processed, you will see an ADD button next to each of those profiles that didn't have an apparent match.
If you have a large GEDCOM and/or have little experience creating or editing profiles here at WikiTree, you may want to delete your current GEDCOM and split it into smaller GEDCOMs.