I wish there was a way to know what items are already under someone's tree so you don't accidentally get them the same thing that someone else did.

I thought about this as well, but then I thought it would be something that could be abused. Like asking someone to tell you what other people have gifted you before the trees are opened up. Kind of defeats the purpose of the surprise.

In my opinion, it's more of the thought that counts. If someone gets a double of something from me and another person, they could just sell the extra and use the sP to buy something else from their WL or whatever.

The person who owns the tree never sees the list. It's only seen by giver.

And telling the receiver would be against the rules like discussing Mysterious Melody.

Yes, I understand. But you could ask someone to go into the gifting page to see the list and tell you what's on it. They could maybe technically make that against the rules, but it would be pretty hard to enforce. If it was against the rules to ask on the site, people who chat off-site could just ask one of their friends there instead.

I get the idea and why it would be useful for some, but I don't really see this being implemented.