Following the imaam until he finishes Taraaweeh

The most correct opinion isthat the number of rak’ahsfor Taraaweeh is eleven, but I pray in a mosque where they do twenty onerak’ahs. Can I leave the mosque after the tenth rak’ah, or is it better to complete the twenty one rak’ahs with them?
Praise be to Allaah.
It is better to stay with theimaam until he finishes, even if he is doing more than eleven rak’ahs, because it is permissible todo the extra rak’ahs, as theProphet (peace and blessings of Allaah be upon him) said: “Whoever prays qiyaam with the imaam until he finishes, Allaah will record it as if heprayed the whole night” (reported by al-Nisaa'i and others. Sunan al-Nisaa'i, Baab Qiyaam Shahr Ramadaan), and because the Prophet (peace and blessings of Allaah be upon him) said: “Prayer at night should be two by two (rak’ahs), and when dawn approaches, pray one for witr.” (Reported bythe seven; this version reported by al-Nisaa'i).
There is no doubt that adhering to the Sunnah of the Prophet (peace and blessings of Allaah be upon him) is better and brings more reward, so long as it is done properly and without haste, but if itis the matter of a choice between leaving the imaam because of the number of rak’ahs or going along with the extrathat he does, it is better to go along with him, because of the ahaadeeth referred to above. At the same time, you should advise the imaam to follow the Sunnah.