Learn Turkish: Ağaç çiçek açıyor mu?

In the present continuous tense, the verb always ends with the suffix -yor. Because of Turkish 4-way vowel harmony, the question particle that follows the letter 'o' is always mu. For any 'is he/she/it doing something' question, the ending pattern is always -ıyor mu?.

Why are there two words, çiçek açıyor, for 'blooming'?

In Turkish, 'to bloom' is expressed with the set phrase çiçek açmak. The word çiçek means 'flower' and açmak means 'to open'. So literally, this sentence is asking 'Is the tree opening flower?'.

Why is çiçek singular? Shouldn't a tree have many flowers?

When a noun is a general, non-specific object of an action, Turkish usually leaves it in the singular form. The tree is performing the general action of 'flower-opening', so we do not need to use the plural form çiçekler.

Where is the personal suffix on the verb for 'it' (the tree)?

In Turkish, the third-person singular (he, she, or it) does not take a personal suffix. We just use the verb root aç plus the continuous tense suffix -ıyor to mean 'it is opening'. The separate particle mu turns that statement into a question.