Is arbre feminine or masculine

- Nouns ending in -e can be either masculine or feminine. For example : arbre, maire, maître, couple, chapitre, livre, bronze, bonze, annuaire, gorille etc. are masculine. 
- Many feminine nouns don't end in -e, such as maison, main, catin, institution, infection, guerilla, cité, télé, moto, auto, gym, guenon... 
- If there is a singular determiner or an adjective before the noun, it may indicate its gender. "Mon", "un", "quel", "le", "ce", "cet", "du" are all masculine. 
But "l'", "les", "des", "mes", "ces" (etc.) won't help you determine the gender of the following noun. 
- Some endings can be often seen in feminine or masculine words, for example : 
words ending in "ière" (policière), "ère" (bouchère), "ette" (tablette), "ienne" (musicienne), "tion" (audition), "arde" (poularde), "asse" (tignasse), "esse" (ogresse), "elle" (voyelle), "ité" (félicité) are often feminine words whereas words ending in "ier" (policier), "er (boucher), "et" (coquelet), "eau" (tableau), "ien" (musicien), "toire" (auditoire), "ard" (traquenard), "eil" (sommeil), "euil" (écureuil) are more often masculine. (The list of these endings is much longer.) 
However, there are many exceptions... 
As a result, when you learn a new word in French, you should always learn its gender in the meantime, searching it in the dictionary if there is no determiner or adjective to indicate its gender when you meet it for the first time.

Le  chien is dog in french