Pio Cristiano Sarcophagus 31551: Detail, Jesus' Triumphal Entry into Jerusalem
See Matthew 21:7-9, c.f. Mark 11:7-10, Luke 19:36-38. As in Matthew and Mark, someone is laying down a cloak for Jesus to ride on. The man in the tree can be either a reference to Matthew 21:8, "others cut boughs from the trees, and strewed them in the way" (though the man has no cutting implement) or to Zacchaeus, who had climbed a tree to observe Jesus' entry into Jericho earlier that same day (Luke 19:1-5).
The Y shape of the tree is also seen on the frontals of another sarcophagus from the beginning of the 4th century in the Pio-Christian and in a Sicilian sarcophagus in the Syracuse Archeological Museum from the second quarter of that century. The early 20th-century restorers of a sarcophagus frontal in the Metropolitan Museum adopted the same shape in their conjectural restoration of the Palm Sunday scene.
This image in full resolution
View the entire sarcophagus frontal
More of Palm Sunday
Photographed at the site by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.