Srimad Bhagavatam Canto 10, Chapter 21, Text 09

SB 10.21.9

gopyah kim acarad ayam kusalam sma venur
 damodaradhara-sudham api gopikanam
bhunkte svayam yad avasista-rasam hradinyo
 hrsyat-tvaco ’sru mumucus taravo yatharyah
My dear gopis, what auspicious activities must the flute have performed to enjoy the nectar of Krsna’s lips independently and leave only a taste for us gopis, for whom that nectar is actually meant! The forefathers of the flute, the bamboo trees, shed tears of pleasure. His mother, the river on whose bank the bamboo was born, feels jubilation, and therefore her blooming lotus flowers are standing like hair on her body.
This translation is quoted from Srila Prabhupada’s Caitanya-caritamrta (Antya-lila 16.140).
In the guise of releasing flowing sap, the bamboo trees are actually crying tears of ecstasy upon seeing their child become an exalted devotee-flute of the Supreme Personality of Godhead, Sri Krsna.
Sanatana Gosvami gives an alternate explanation: The trees are crying because they are unhappy at not being able to play with Krsna themselves. One may object that the trees in Vrndavana should not lament for that which is impossible for them to obtain, just as a beggar certainly doesn’t lament because he is forbidden to meet the king. But the trees are actually just like intelligent persons who suffer when they cannot obtain the goal of life. Thus the trees are crying because they cannot get the nectar of Krsna’s lips.
Srimad Bhagavatam Canto 10, Chapter 21, Text 08
Srimad Bhagavatam Canto 10, Chapter 21, Text 10