So sorry the little guy died. It sounds to me like there's not a whole lot more you could have done for him. Good on you for making such an effort!

This forum is a fantastic resource for caring for frogs. If you choose to get a White's tree frog, don't miss the care sheet on here if you haven't seen it already. Also I found when I was researching that most care sheets online seem to have pretty sketchy info on the substrate for White's tree frogs; I didn't find out until I came here that the usual recommendations for bark/sphagnum moss etc. are not good for White's tree frogs. The knowledgeable guys on here recommend a false bottom or drainage layer to keep the substrate from getting soggy, and a substrate of Eco Earth/Plantation Soil which is safe for them. I hope I don't sound too much of a know-it-all since I don't even have our frog yet, I'm just repeating what I've read!

Best of luck and once again, sorry you had a bad experience with your little guy.