Creating the Tree
First, we're going to create the top, leafy part of the tree. Using your ellipse tool set on Paths only, create a large oval like so.
Now, using your pen tool, alter the paths enough to make an interesting tree shape. It can really be as round or oval as you want, and it can be a bit asymmetrical, but remember, kitsch is relatively simple, so don't go too crazy.
Fill your path with whatever color you want. Keep in mind that kitschy artwork is generally muted colors in mustard browns, mint greens, brick reds, terracotta orange, and olive drabs. This doesn't mean that you have to stick to these colors, but it does reflect the time period relatively well. Delete the path after you're done.
Now, we'll create the trunk. The easiest way to do this is to first create a triangle with the pen tool that starts well below your tree, but then extends about 3/4ths of the way up into it.
After you get it positioned to where you would like it, use the pen tool to round the top and widen it a bit like the example below.
Fill the path as you did before with a color of your choosing.
Now, create some branches from the trunk that extend into the tree. You can use the same method you did to create the tree trunk. Feel free to add any embellishments to your tree that you like. These can be leaves or knotholes or bark textures. Just remember to keep it simple!