Answer: The usual causes for non-blooming are immaturity, insufficient sunlight or over-fertilization. Your tree is certainly old enough to bloom. It should be receiving full sunshine (if not you might want to move it to a sunnier location). Withhold fertilizer (too much nitrogen will result in lots of vegetative growth at the expense of flowering). If correcting the growing conditions doesn't result in blooming, I'd prune the branches back a bit. Pruning usually encourages new wood and in this case, new flowering wood.
Best wishes with your trumpet tree!
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