A sycamore tree - See this described in the notes at Luke 17:6.

He ran before - The shortness of his stature was amply compensated by his agility and invention. Had he been as tall as the generality of the crowd, he might have been equally unnoticed with the rest. His getting into the tree made him conspicuous: had he not been so low of stature he would not have done so. Even the imperfections of our persons may become subservient to the grace of God in our eternal salvation. As the passover was at hand, the road was probably crowded with people going to Jerusalem; but the fame of the cure of the blind man was probably the cause of the concourse at this time.

And he ran before,.... Jesus, and the company that was with him; so very desirous was he of seeing him:
and climbed up into a sycamore tree to see him: which sort of trees were very common about Jericho: hence we read of, , "beams of sycamore" in Jericho, which those that were strong took up in their arms, and the owners stood and devoted them to God (g); and among the things which the men of Jericho did, this was one, that they permitted the branches of trees devoted to sacred uses, and of the "charub" tree, and of the "sycamore", to be cut down and used (h). This sort of trees used to grow in plains and valleys, as appears from some passages of Scripture, 1-Kings 10:27 and from Jewish writings (i); and certain it is, that Jericho was in such a situation. Josephus (k) says, it was seated in a plain; and Strabo says (l), that Jericho is a plain surrounded with mountains; to which agrees the account that (m) Justin gives of it. There is a valley, which is enclosed by mountains on all sides, as with a wall, like a castle; the space of the place is two hundred acres, and it is called Jericho. Hence we read of the plains and valley of Jericho in Scripture, Deuteronomy 34:3 so that it is very probable sycamore trees grew there in great plenty; though the place was more famous for palm trees: hence it is called the city of the palm trees, Deuteronomy 24:3 which the Targumist, in both places, interprets, the city of Jericho: to which agree the accounts given of it by Pliny (n), Strabo (o), and Justin (p), who all affirm, that it abounded with palm trees; and the latter says also with balsam trees, from the sweet smell of which it might have its name: so the Jews say (q), the ointment of balsam is called the ointment of our land, because it grows in Jericho, and because of the smell of it, it is called Jericho; though some think it has its name from the plain, being in the form of a half moon; the moon, in the Hebrew language, being called (r). This tree seems to have been without the city: and indeed, according to the Jewish canon, it ought to be, which runs thus (s);
"they set a tree at a distance from a city, twenty and five cubits, but a "charub tree", and "sycamore", fifty cubits.''
The reason of the greater distance of the latter is, as one of their commentators says (t), because their branches were large; and this is the reason why Zacchaeus went up into one of these trees, because it was large and able to bear him, and tall, from whence he could have a full view of Christ:
for he was to pass that way; or rather, "pass by that"; for the word "way" is not in the text; and the sense is, he was to pass by that tree; or "under" it, as the Arabic version renders it. The tree stood by the road side, in which Jesus came, for which reason Zacchaeus made choice of it, as fit for his purpose.
(g) T. Bab. Pesachim, fol. 57. 1. & Juchashin, fol. 69. 1. (h) T. Bab. Menachot, fol. 71. 1. & Pesachim, fol. 56. 1. (i) Misn. Sheviith, c. 9. sect. 2. (k) De Bello Jude. l. 4. c. 27. (l) Geograph. l. 16. (m) Hist. l. 36. c. 3. (n) Nat. Hist. l. 5. c. 14. (o) Ut supra. (Geograph. l. 16.) (p) Ib. (q) Gloss. in T. Bab. Beracot, fol. 43. 1. (r) Vid. Masium in Josh. c. 2. p. 37. (s) Misna Bava Bathra, c. 2. sect. 7. (t) Bartenora in ib.

sycamore--the Egyptian fig, with leaves like the mulberry.

And running before - With great earnestness. He climbed up - Notwithstanding his quality: desire conquering honour and shame.