For 20 Playfish coins, the Tree House in Pet Society gives you another room to decorate. Here is the outside view of the tree house. The tree can be placed in your garden or a regular room in the house:
One reader, Julie loves the tree house. She likes the extra room to play with and she thinks it's a bargain compared to the Secret Garden which requires the purchase of 3 fairies that total 65 Playfish cash coins.