Albert Barnes Commentary Nehemiah 8:15

"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 branches of wild olive, and myrtle branches, and palm branches, and branches of thick trees, to make booths, as it is written." — Nehemiah 8:15 (ASV)

The mount - The “Mount of Olives” is probably intended.

Pine branches - Rather, “branches of the wild olive.” The actual trees named by the Law may have become scarce. It was probably considered that the spirit of the command was kept if branches of trees similar in general character to those named in Leviticus were employed.