What should I call a poset with the property that each element has a unique predecessor?

(I'm actually interested in the special case in which there are no infinite descending chains.)

CLARIFICATION: I mean each element has a unique immediate predecessor.
As you go higher up there can be branching, but never collapsing. That is, I don't want to allow $a < z$ and $b < z$ with $a$ and $b$ incomparable; but I am happy with $a< y$ and $a< z$ with $y$ and $z$ incomparable.