The song is from season 4 episode 14 of MLP:FiM | Full Mix: http://goo.gl/xulKe1 | Reprise: http://youtu.be/TVJdpJw1jio | ♫ Lyrics:
( You can support the show here: https://itunes.apple.com/us/tv-season/my-little-pony-friendship/id811603835 )
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[Fluttershy]

There's music in the treetops
And there's music in the vale
And all around the music fills the sky
There's music by the river
And there's music in the grass
And the music makes your heart soar in reply
[vocalizing]

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"My Little Pony" is owned by Hasbro,
"MLP: Friendship is Magic" is created by Lauren Faust.