what is this tree please?

what is this tree please?

Observation - what is this tree please? - UK and Ireland. Description: the blossom appears just before the leaves and later there will be small orange fruits like mirabelles but when I ate one last year it caused stomach aches and diarrhoea. The tree has grown considerably over the last ten years. It has a blackish shiny bar

the blossom appears just before the leaves and later there will be small orange fruits like mirabelles but when I ate one last year it caused stomach aches and diarrhoea. The tree has grown considerably over the last ten years. It has a blackish shiny bark.