I have conquered Irish Skills Tree last week at level 11; I would like to know can I go any further than this level as I'm being told I must aim to reach level 12.
"Levels" on Duolingo are simply a reflection of the number of XP earned. If you repeated the very first lesson 3,000 times, you would earn 30,000 XP, and reach level 25.
There are over 17,000 exercises in the Irish course on Duolingo - you have earned 3245 XP, so you have probably done between between a quarter and a third of the available exercises (probably less, because you will have seen some of them more than once).
Just keep doing strengthening exercises - either individual skills, or the whole tree. Mix things up with some timed practice. There is still some chance that the Irish course will be expanded with Tree 2.0, but there has been no word on that for a long time.
Hey knocksedan, just curious how you know that there are 17,000 different entries for Irish. This is encouraging as I finished the tree awhile ago, and still haven't noticed much repetition, but I fear that I will run out of novelty soon..
I didn't remember exactly where I saw those numbers, but sometime last year, Oisín Ó Doinn, who is one of the contributors to the course, wrote a report on the Duolingo Irish course - there is a link to his report in this discussion.
Currently the Irish course contains c. 2000 of the most commonly used words in the Irish language. These words are used to generate over 19,000 unique sentences (Duolingo.com, 2016a)
The 2016a reference is a link to the Duolingo incubator, but the link itself doesn't seem to work. A working link to the incubator does show that the "Beta Week 18: Looking forward to 2015" post, included End of Year statistics such as "Total no. of sentences: 16,920" and "Current no. of words: 1711"