Trees

Five cards dealt. Betting round. Players freely exchange cards with other players, always receiving the same number of cards as is traded away. When all players are finished trading, there is a final betting round. Best hand wins.

The only rule when trading is that the number of cards traded must be the same as what is received (“Who wants to trade 3 cards?”, “Does anybody want to trade 2 cards?”).

This trading round continues until no pair of players wants to trade any more cards. There is a second betting round, followed by a showdown.

Strategy
The best thing to do is remember which cards have been given to what players. Players interested in trading initially three, and then two, and then one card are most likely putting a straight or flush together. Passing a pair is obviously out of the question, but passing consecutive cards (for example, a Two, a Three, and a Four) or cards of the same suit to the same player may not be strategically wise.