Hello,
The two corals don't really look much alike. When closed Sun Coral (Tubastrea faulkneri) looks similar to a colony of Zoanthids. Tree Coral (Dendronephthya) on the other hand looks more like a colorful/fuzzy Colt Coral (Cladiella sp.) with a uniform trunk to the base. If you Google the scientific names you will find some excellent images of each.
Regards,
Kevin