any creative ideas ?

Make a cone shape of green fondant. Get tiny sharp scissors and snip the fondant all the way around up to the top. It makes a fir type tree!

I have used pretzels and used the leaf tip with royal icing. If you look at my pics, they are on the cake with the cars. You can use the big rod pretzels for large trees, and the little stick pretzels for small trees. I piped the icing on and then stuck them in foam to dry.
That's my suggestion, I'm sure there are tons of other ways to do them-lots of creative people here .
Good luck!

It could depend on how mini you want them, you could pipe small trees and decorate them with red dots if you want them for Christmas. Otherwise another idea is a small ball/cone shape and twisted rolls for a trunk then a thimble for a pot stand. But as Keira suggested you can make a small cone shape and make little cuts with a pair of scissors then if you want a decorated tree you could pipe coloured dots on that as well.

ice cream cones (the sugar ones that are brown) you "cut them down" to the size you want and cover them with BC frosting using a star tip.... it works out very nicely!