Just no.

@Daz Dvergar  
Do you wanna see the rabbits, David?
 
(sorry/not sorry.)

NO

It’s David the Gnome all over again!

@CommanderX  
Agreed

Good thing this is completely False.

They plantedd the tree :\

If we want to get theorizing, it’s not that much of a leap to imagine that if there’s one condition that turns ponies into trees, there might very well be a different condition that turns them into different trees. Or perhaps, as I’ve seen theorized in the other comments, an offshoot or mutation of regular swamp fever could do this.
 
Or alternatively it might be that the swamp fever had an odd reaction after coming in contact with strong earth pony magic and did not end with a transformation into the usual type of tree, but something more related to its victims’ personal magic. (It’s a popular guess, and one that I hew to, that the members of the Apple family are to earth ponies what Twlight, Sunset, Starlight, Starswirl and company are to unicorns or Rainbow Dash is to pegasi, no stretch to assume the same applies to the Pears. And on that note, might ponies like Pinkie’s relatives turn into rocky or crystal trees? Theorizing is fun!)
 
I mean, I know that those two trees are most likely sprouted from the seeds they planted at their wedding, but fandom theorizing is always a fun pastime.

To be fair, those two did plant two seeds that grew into those trees, so I don’t think this theory is accurate. Though I can’t deny that’s one dark theory you got there.

Interesting..  
add list theory

I thought acorn becomes tree?  
Double-D lied!

Who knows? Maybe they did something with the seeds that stopped them from becoming SF trees and instead became apple and pear trees that weren’t infectious? Or maybe there are apple and pear offshoots of the swamp fever plant?
 
Its not that hard to explain away the seeds they planted and replace them with the parents themselves. Its just a question of DO you want to do that? Is this really the fate you want for them?

It’s joke

YOUR IDEA IS BAD AND YOU SHOULD FEEL BAD!!!

They planted those trees.
 
And the disease will turn you into a tree that spreads the disease. Pear and apple trees don’t do that.

Aw, that’s cute. I think I should reward you with a time-out.