Planting a tree takes time and effort. Most people do not plant a tree with the intention of sitting under its shade immediately. Trees take years to grow before they will provide shade. In fact, most people won't be around to enjoy the shade of a tree they have planted.
The true meaning of life is to do something positive, like planting a tree, but not to expect to gain anything from it. The reward is the knowledge that someday someone will be able to sit in its shade.
Have you planted a tree lately?