Many years ago for an outdoor party I made some mason jar luminaries to hang throughout the trees. They are overall pretty simple (minus the process using a ladder to hang them). This project would probably work better with lower hanging trees, but any will work as long as you have a tall enough ladder.
-Mason Jars (or a similar canning jar)
-24 guage wire
-Gravel or Sand
-Pliers
-Wire Cutters
-Tea Lights
-Twine
1.Take your jars and make sure they are clean. You can set the lids aside, you won't be using them for this project. Twist a small loop about 6 inches into the wire. Wrap the wire around under the lip, and twist another twisted loop on the other other side. Twist the two loose ends together. Cut the wire
2. Cut a 6-7'' piece of wire. Twist one end in one of the loops. Arch it over (this is your hanger) and twist at the other end.
3. Fill the bottom with your gravel or sand (you can also use those glass stones you find in the floral section) and place a tea light in the jar. Make sure the wick is standing up, so that you will be able to light it easily.
4.Then use a ladder to hang twine from a tree. Loop the twine through your wire hanger and tie a sturdy knot. The twine allows you to adjust the height of the lights.
Once it's dark, light them for a magical firefly effect.
They can also be hung on railings, placed along the walkway to an event or set on a table (These last two options will not need the wire).