I'd make an educated guess that A) You do not have a new cultivar on your hands and that B) This plant will eventually come to resemble pretty much any other 'Autumn Brilliance' serviceberry. New growth is heavy, new stems are relatively thin and weak, and together, the plant ends up looking somewhat weepy. I'm reminded of young American elm trees which, despite the fact that left to their own devices, ie. no Dutch elm disease-would go on to become majestic trees with clear trunks for forty or more feet and a dead=straight trunk, look nothing like this at first.

I have zero interest in wiring up or splinting plants. In virtually every case of this I've seen, the end result is less than satisfactory and features weak stems and ungainly growth. YMMV.

LOL Thanks Tom. I didn't really think I have a new cultivar. :)

if i just planted a mail order plant.. a few months ago.. i would simply be happy its alive ...

have you spoken to your seller?

if does not surprise me that fresh new green growth is weepy .. but after just a few months.. i would not conclude its form is weeping ... is it in full sun??? .. if not.. how many hours ...

did you throw fert in the planting hole???

complaints of a seller sending too big a plant.. are rare .. lol ...

you said: I wanted the shorter one because I actually would like a multi stemmed bush

==>>> looking at google pix ... i dont understand why you chose this one, if you want a bush ... i suspect the words mean different thing to each of us ... maybe you could expand on your dreams ...

ken

https://www.google.com/search?q=Autumn+Brilliance+amelanchier&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiEtfCb18DNAhWq5IMKHVJDAhYQ_AUICCgB&biw=940&bih=745&dpr=0.9

No fertiliser, even though the plant arrived with a packet of fertiliser that the seller suggested I place in the planting hole. It is in part shade.

As for the reason I chose this is I've grown Autumn Brilliance before - but from a much smaller sapling, and alas, in a different city and state.

Those pictures almost all illustrate exactly what I want - perhaps I shouldn't have used the word "bush". Blame it on not yet having finished my first cup of tea of the day.

Widdringtonia, you will very likely be pleased in getting plenty of basal suckers from your Amelanchier. What I'm getting at-and what it seems you already know-is that in nature, these things never really exist as single-trunk specimens. And once planted out, it is either maddening or gratifying-depending on your goals-to see the constant generation of these basal suckers. You'll get the multi-stemmed plant you desire, I warrant.