I don\’t know what kind of tree or bush this is or how to prune it
I have attached a picture, it just fell over like this last week
Certified GKH Gardening Expert
It may be a plum, or my best guess is a cherry plum (Prunus cerasifera), or another species from the genus Prunus. Did it produce flowers and fruit?
The upright portion appears okay, and if you want a single stem tree, you could prune off the fallen/leaning portion at the base and leave the upright.
But if you want to save the leaning portion, you will have to get in there and determine if the stem or stems are broken or just leaning due to overburdened weight distribution. If not broken you may be able to reduce some top weight or branch end-weight by pruning it back some, which may allow it to pop up into better position. That along with some thinning of excessive number of stems and you may be able to straighten it up. If there are broken stems it will best to remove those at the base.