John 12: 13 Took branches of palm trees, and went forth to meet him, and cried, Hosanna: Blessed is the King of Israel that cometh in the name of the Lord.

Ps 118: 26 Blessed be he that cometh in the name of the LORD: we have blessed you out of the house of the LORD.

Ne 8:
14 And they found written in the law which the LORD had commanded by Moses, that the children of Israel should dwell in booths in the feast of the seventh month:
15 And that they should publish and proclaim in all their cities, and in Jerusalem, saying, Go forth unto the mount, and fetch olive branches, and pine branches, and myrtle branches, and palm branches, and branches of thick trees, to make booths, as it is written.

Lord God liberated nation of Israel from the slavery of Egypt. For the memento of this Israelite must live on booths in the time on the feast of tabernacles. Palm tree is a sign of joy and victory. When Jews heard and saw that Jesus is coming to Jerusalem, some people took branches of a palm tree. They went out to meet Jesus and cried, Hosanna: Blessed is the King of Israel that comes in the name of the Lord. They show to Jesus the sign of joy and victory in theirs hands, which were branches of a palm tree.