The process of putting Christmas lights on an outside tree can vary depending on the type of tree and the size of the tree. Generally, you will need to plan out the design of the lights and then use a ladder to reach the upper branches of the tree. You can start by stringing the lights along the lower branches of the tree and then gradually work your way up to the top. Make sure to secure the lights tightly so they don't fall or become tangled. Additionally, you may want to consider using an extension cord or a generator to power the lights.