Extension ladders extend upward to reach higher places. Extensions are retracted when not in use so the ladder can be stored more easily. When pruning trees, sometimes even a telescoping tree trimmer isn't long enough to reach all the branches. In these cases, an extension ladder is a good way to get you high into the branches to trim the limbs and keep tree healthy.
Set the ladder up against the tree, and push the section of the ladder closest to you upward. Watch for the brace to catch as each rung goes by. Push it up as high as you want it. Some taller extension ladders have a rope to pull that aids you in raising and lowering the ladder.
Check to see that the brace caught securely on the ladder rung.
Adjust the ladder to a stable position so both legs are on solid ground. Make sure the ladder is near the branches you want to trim. This will allow you to safely work without reaching too far.
Have someone hold the ladder. Even through you have the ladder in a good position, it is always a good idea to have someone hold a ladder from the bottom. They can keep the base from shifting under your movements.
Climb the ladder to get to the branches. Use a tree trimmer if you need to reach out into the branch to trim it. Not all branches have to trimmed close to the tree's trunk. If it is a diseased limb, you usually can cut the limb about 12 inches below the diseased area. If you are cutting the branch off next to the trunk, then a handsaw is easier to handle.