Decorate the walls. Put up wallpaper with a tree pattern if you have finished walls. Paint “Welcome to the Tree House” on an unfinished wall. Another option is to paint a mural on one wall or extending all the way around the basement. You can paint any scene featuring a tree house that you like. Use premade, stick-on murals on finished walls.
Use furniture to fit the theme. Add toy bins and a bookcase for storage and a kid-size table and chairs. Paint branches and leaves or entire trees on the furniture. This is a fun project you can do with the kids and is a way to give mismatched pieces a uniform look.
Add tree-house accents. Put up a plastic, Styrofoam or cardboard tree in a corner. Drape Christmas lights over for some twinkle. Install a climbing wall and paint it to look like a tree. Bring in accent pillows, a rug, curtains and a lampshade that have a tree or leaf pattern.