Pineapples don't grow on trees nor do they form trees, they are bromeliads native to central America and can attain about 5 foot in height. Some of the ornamental varieties get no bigger than 18" and have very very spikey leaves.

If you mean the Cytisus battandieri, You can trim any new branches down by about half, after flowering, but with all 'brooms' never cut back into old wood, they don't regenerate.