As was implied by the last post of this title the story of Jesus calling Zacchaeus from a tree symbolizes the fruit of the Kingdom being brought in. The following passage only helps to confirm this symbolism:
And Amaziah said to Amos, “O seer, go, flee away to the land of Judah, and eat bread there, and prophesy there, but never again prophesy at Bethel, for it is the king’s sanctuary, and it is a temple of the kingdom.” Then Amos answered and said to Amaziah, “I was no prophet, nor a prophet’s son, but I was a herdsman and a dresser of sycamore figs. But the LORD took me from following the flock, and the LORD said to me, ‘Go, prophesy to my people Israel.'” (Amos 7:12-15)
Here, again, is the passage from Luke:
And he was seeking to see who Jesus was, but on account of the crowd he could not, because he was small of stature. So he ran on ahead and climbed up into a sycamore tree to see him, for he was about to pass that way. And when Jesus came to the place, he looked up and said to him, “Zacchaeus, hurry and come down, for I must stay at your house today.” So he hurried and came down and received him joyfully. (Luke 19:3-6)
Just as Amos was a herdsman and a dresser of sycamore figs who had come to prophesy so Jesus came as a prophet to rescue his lost sheep and dress the fruit of his vineyard. In the Gospel of Matthew 21:19 Jesus curses the deceptive fig tree (it covered its lack of fruit with leaves) because it bore no fruit – here Jesus brings salvation to the faithful young man in the sycamore tree.