Wild cherry sapling leaves going brown

Hi all.
I have been growing a wild cherry and recently the leaves have been going brown, as you will see in the photo. It’s now affecting every leaf on the tree.
I’d be grateful for any advise on what is causing it and how to rectify it.
I’m keen to keep the tree in a pot for as long as possible - is this feasible?
Sorry for the ignorance, I am a complete novice!
Thanks.

 

I can't really see the size of the pot but they dry out pretty quick, are you watering it regularly? It could be leaf scorch which is due to lack of water. I'd have a look to see if it's full of roots and move it to a bigger pot.

 

I think it’s a 10 litre pot.
It’s only been in that pot for a couple of months, so it shouldn’t be full of roots yet should it?

 

Probably not, but I would just take it out and have a look at the roots anyway, the leaves to me look like under watering but there's a possibility it's over watering. It is feasible to keep going in pots but if you plan to plant it out sometime I would do it sooner rather than later.

 

So all of the leaves came off, but it’s recently started growing some new buds, so that’s positive!
However, there is some growth at the bottom of the tree now, as pictured. should I be removing this? Thanks.