I love the smooth transition and chronology of this piece. It started out with the two characters as children playing by/under the tree, then they got married under the tree, and finally when they got older and perhaps had children, the tree reminded them of their love.
The only confusion a reader (such as myself) might have with this piece would be what kind of tree it is. So my advice: be more descriptive. Most likely the tree is a Christmas tree, but it seems too fairytale-like and a bit far-fetched if it was a Christmas tree and they got married beneath it. So be more descriptive :)
As for imagery, it was beautiful. The emotion- what I got was... happy (?) so I don't quite get why you placed this under 'sad poems'

"Mary replies, "It's a miracle!" as her heart
lights with glee.
And they smile at me, to me!
And I'm heavenly sure that they love me,
Even if it is only for an instant - a heavenly
second."

I love the dialogues, and in the end^^^ I was expecting something sad. Perhaps the tree died? And it seemed hopeful especially with that last line. Hm, maybe I'm not thinking right today, but I know you have a reason here and I respect you for that.

Before I forget, I suggest you do not add the note in the parenthesis in the beginning. Do not spoonfeed the reader. Make them think. It would be evident with the aid of the title and narration that it's the tree speaking, so I suggest you remove it :)

Hm, note this aswell:

"The transparent ghostly wind, now she
hums,"

'Wind' is obviously transparent, so I think it is unnecessary to use that adjective. Choose something more interesting, and back to my advice: be more descriptive. The imagery is there but this needs more descriptive words.
Overall, I really enjoyed reading this. Just a few tweaks would help. Keep writing :)
-X