Cut a point on one end of a 2-by-2 wooden stake that is about 2 feet long. Make a notch across one side of the stake a few inches from the other end.
Place the stake a few feet away from the tree on the opposite side from the way the tree is leaning. Angle the stake away from the tree, with the notch facing away from the tree. Push or pound the stake about a third of the way into the ground.
Cut an old garden hose the length you will need to fit around the trunk of the leaning arborvitae.
Cut a length of coated clothesline wire to fit around the trunk of the arborvitae plus a few extra feet for anchoring.
Run the coated clothesline wire through the length of garden hose with several inches of wire coming through the other end.
Wrap the length of garden hose around the arborvitae trunk. Twist the protruding few inches of wire back around itself several times to secure the hose and wire.
Pull gently on the wire to bring the arborvitae back into line. Wrap the wire around the stake, making sure that the wire is seated in the notch. This keeps the wire from slipping off the stake.
Twist the wire back around itself to secure it to the stake.