If the tree is killed, individual leaves die in 1d10 rounds.
The singing tree appears to be a normal deciduous tree with uniquely shaped leaves. Each leaf sings with a lovely voice, the hundreds of them blending into a beautiful chorus. If hungry, the tree joins the chorus, adding its own bass line.
When the tree uses its bass line, all mammalian creatures within 100 yards must roll saving throws vs. spell; those who do not succeed feel compelled to stop for a bit and rest in the shade of the tree. When a potential victim rests beneath the tree, several leaves fly off the tree to attack.
In the wild, singing trees grow in secluded places and use their music to lure unintelligent animals. The tree’s leaves vibrate in the wind; combined with their natural magic, this makes a lovely sound. Each leaf has its own “voice,” and the music is indescribably beautiful. When the tree adds its lower tones, the song becomes very attractive and calming.
That's true. It's actually a pretty powerful sleep effect since wounding doesn't end it (more like a symbol of sleep than a sleep or deep slumber spell). Want to go that nothing nonmagical can awaken the victim for a set duration or else make it a normal sleep effect but that isn't disturbed by the leaves?I dunno about fascination. It appears to be a genuine sleep effect--one that isn't broken by taking damage.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.