Solved Mystery plant, can anyone help please?!

Hello!
Can anyonehelp me identify this little guy please?

My dad had it in a pot and didn't know what it was either. I've had no luck on Google so far. The first thing that came up was 'identifying Japanese knotweed' (scary) but from looking at the leaf shape I'm pretty sure that's not what it is.

If anyone recognises it I'd really appreciate some help!

Thank you in advance
Aimo

 

Looks like a weedy willow tree.
Salix caprea...a gift from the birds.

Rest assured it is definitely not Japanese knotweed.

 

Thank you very much @Silver surfer! Glad to finally be able to put a name to the leaf (And very glad it's not the dreaded JN)

 

Actually a gift from the wind.
Nextdoor neighbour has a large tree, it's like its snowing sometimes.

 

Hi @Aimo I would suggest putting it in a slighter bigger pot so it's centre is in the middle or if you put it in the ground support it with a plant state to help the stem to develop properly