In the Zoroastrian religion, Trees are earthly embodiments of Ameretát “Immortality, Deathlessness, Life ever-lasting.” Specifically ancient trees, evergreens and healing herbs exemplify Immortals and Immortality.
Zoroastrian Priests are enjoined in the Avesta (book of hidden, unknown wisdom) to hold sacred branches of evergreens or fruit trees in the hand while reciting the sacred Avestan verses and conducting religious ceremonies.
As powerful life symbols, trees are venerated in many sacred Avestan verses, See Yasna 16.89, 17.12, 17.16 for example.
Forests and woods are considered to be the home of god-beings. The Avestan word for “god, good fortune or blessed/lucky portion” is “bagá and/or baγa,” (Compare with Russian *bȏgъ.) The Persian word for “lush garden with trees” is “bágh/báγ” derived from the same Avestan root for god/good fortune.
Furthermore, in Zoroastrian sacred poetry there is a close connection between “trees and truth.”
For example in the 99th verse of the hymn to Fra.vashis or “Primordial Ideals/Guardian Spirits,” The sage ruler Vištáspá, searches for truth in trees/woods and ancient rocks drû-ča paûrvãn-ča. (Kind reminder of Didier Calin, See also Watkins)
The Persian word for tree, deraḵt comes from Avestan dauru, Proto Indo European *dóru, Old Slavonic drŭva “wood,” Gothic triu, Old Norse tré, Old English tréow “tree.” (See Didier Calin)
The close link between trees, seers, prophecy/oracles and truth is demonstrated for example in the süd-kar gathic commentary of Yasna 31, wherein the ages of the world, understanding the past and forecast into the future is illustrated via Tree symbolism.
In the poetic gathas, “lushness, verdure and power of growth” are ascribed to artistry and excellence of Mazda “god of creativity and genius,” (See Yasna 48.6, 3rd rhymed verse line.)
There is also mention of a support holding (deretá) the earth (zám) below and nebulous, celestial skies (nabávß) above, in the poetic gathas (See Yasna 44.4, 2nd rhymed verse line.) The gathic verse is very similar to Rig Veda:
8.041.10e ajó ná dyā́m ádhārayan
8.041.10f nábhantām anyaké same
The reference to a cosmic or archetypal tree is repeated in the Avestan hymn to Rašnü, the god force of “rightness, accuracy and truth.”
Rašnü is paralleled by Latin rectus, Gothic raihts, German recht, (See Emile Benveniste, although there is no absolute certainty/consensus among linguists regarding the etymology of Rašnü.)
In verse 17, we read of the cosmic or archetypal tree. The tree has the combined seeds of all plants van-î vaß-tôḵmag or van-î har.vißp-tôḵmag. It grows in the middle of the wide-shored ocean (vôurû-kaša.) It is an “all-healer” or “all-remedy tree” (vîßpö-biš,) that drips the immortal nectar of haômá.
The mythical bird Sîmorḡ is said to perch on it every year to mix its seeds with water, which Tištar (Tri-star Sirius) then rains down on all the regions of the world, thus propagating all kinds of healing plants. Öhrmazd has planted the “sacred white Höm (Avestan haôma), near the all-remedy tree, in order to keep away decrepitude and old age (zarmān) by imparting immortality to anyone who partakes of it.
ýat-čit ahi rašnvö ašáum
ûpa avãm vanãm ýãm saænahä
ýá hi-štaitæ maiðîm zray.ang.hö vôurû-kašahæ
ýá hû-biš ereðwö-biš
ýá vaôče vîspö-biš nãma
ýãm upairi ûrvaranãm
vîspa.nãm taôḵma ni-ðayat
Whether thou, O virtuous Rašnuu! art on the tree of the eagle/ sîmorḡ, that stands in the middle of the wide-shored sea/ocean vôurû-kaša, that is called the tree of good remedies, the tree of powerful remedies, the tree of all remedies, and in which is held the seeds of all/everything!
European travelers encountered many sacred trees in Iran even into the Islamic times. Marco Polo (I, p. 127) recounts the fabled “cypress of Zoroaster” in his memoirs. The venerable attitude toward “trees and sacred spots” has continued in Iran to the present day, but with the transfer of devotion to Muslim saints, especially Twelver Shiʿites.
Yet it is important to add that under the Zoroastrian jurisprudence, trees enjoyed a wide range of special protections, care and great reverence. However, after the fall of Zoroastrian state, this legal protection has all but disappeared. This has unfortunately resulted in continuous deforestation of the land and great indifference to the natural environment.
For all who might be interested, Didier Calin provides a comprehensive etymology of tree (/oak) here:
PIE *dóru, G *dréus, Ht. tāru ‘wood’, allantaru- ‘oak’; Luw. tāru; HierLuw. /tāru/; In. dâru, G dróḥ; Av. dauru, G draoš; Gr. dóru ‘tree trunk, spear’, drũs ‘tree, oak’; Alb. dru ‘wood, tree’, drushk ‘oak’; OIr. daur; W darw ‘oak’; OSl. drŭva ‘wood’; Toch. A/B or ‘wood’; from a derivative *dréwom: Goth. triu; ON tré; OE trēow (> E tree); Lith. drevė and Lv. drava ‘apiary’; Lv. drāva ‘natural hollow in a tree where bees nest’; from *dérwom: ON tjara; OE teoru (> E tar); Br./W derw ‘oak’; OSl. drĕvo; Lith. dervà and Lv. (dialectal) derva ‘tar’; from *dórwo-: Lv. darva ‘tar, pitch’.