They look like the old Britains Trees modular pine trees. A range of plastic farm, garden and wildlife toys/miniatures from the sixties and seventies. I have acquired a huge pile of them over the years, as they are perfect for wargaming use.
I have several of these small pines and they have stands exactly like that. The trees are made up of branch levels, which fit on top of each other with nubs that so form the trunk of the tree. The bottom layer slots into that brown plastic base.
If I can find them, I'll try and take a picture tomorrow...