I wonder if any body can identify this fruit?

[peter bendall]

I wonder if any body can identify this fruit 
  they have been growing 3 or 4 years at the bottom of
  the garden. It is 3m tall (10ft) now....
It is a fruit, apple shaped though 1 to 2 cm, 1/2-1 inch
  in size. Usually green and,when ripe,yellow and same
  size
It has 'spikes' 5cm (2 inches) long as well!

I did photos, they at at

   http://homepage.schleswig-holstein.de/cbendall/fruit.jpg

and the tree at

   http://homepage.schleswig-holstein.de/cbendall/tree2.jpg

and the spikes, 

   http://homepage.schleswig-holstein.de/cbendall/tree3.jpg

I wonder if there is a type of apple!!!!

peter bendall