Next we will create the ground with the Paint Bucket tool. Create another layer and select the marquee select tool. Select the ground around the tree. There should be "marching ants" on the floor. We will use the paint bucket tool to fill this selection in.
Now use the paint bucket tool to fill in the color. Press ctrl + D to get rid of the selection. Since we want the roots of the tree to show up in front, we will drag the ground in the layer palette below the tree cut out. Name it grass.