Mother of the bride

Who's this behind the blooming pair
With that extravagant dress
and flowers in her hair?

Once the image of the two crab apple trees as bride and groom got into my mind, I couldn't help seeing the other trees and shrubs as part of the wedding party. To one side is a lovely weeping birch -

- But who's quietly standing over there
With drooping branches
And a melancholy air?

Perhaps it's a bridesmaid or a rejected suitor?