Hmmm - these folks tell you it is rare without telling you what it is?...
It is a katsura, Cercidiphyllum japonicum.
I would say it is moderately unusual.
I gave my father one for his birthday many years ago.
The leaves look rather like those of the Judas tree or redbud, Cercis siliquastrum - hence the specific epithet 'cercidiphyllum'. But that has alternate leaves - whereas those on katsura are opposite. The habit of the whole tree is different, too: that of katsura is much more symmetrical and organized; that of Judas tree is more, shall we say, 'free-form'.
Hi thanks Mike, a random gentleman (a fair few months back) came and told me, to be fair, the name, however it went in one ear and out of the other. Today, strangely a man knocked on the door and said to my wife it was very unusual but didn't say what it was , strange as it sounds.