Here's why:
* Long vowel sounds are typically represented by the vowel letter itself, or a vowel letter followed by a silent 'e'. For example, "tree" would have a long 'e' sound if it was spelled "treee".
* The vowel sound in "tree" is a short 'e' sound. It is pronounced as the 'e' in "bed" or "pen".
Therefore, "tree" is not a long vowel word.