is that tree is a large plant, not exactly defined, but typically over four meters in height, a single trunk which grows in girth with age and branches (which also grow in circumference with age) while decibel is decibel.

As nouns the difference between decibel and octave

is that decibel is decibel while octave is (music) an interval of twelve semitones spanning eight degrees of the diatonic scale, representing a doubling or halving in pitch.

is that decibel is a common measure of sound intensity that is one tenth of a bel on the logarithmic intensity scale it is defined as db = 10 * log_{10}(p _{1}/p _{2}), where p_{1} and p_{2} are the relative powers of the sound while phon is (acoustics) a unit of apparent loudness, equal in number to the intensity in decibels of a 1,000-hertz tone judged to be as loud as the sound being measured.