  We study information gathering in ad-hoc radio networks. Initially, each node
of the network has a piece of information called a rumor, and the overall
objective is to gather all these rumors in the designated target node. The
ad-hoc property refers to the fact that the topology of the network is unknown
when the computation starts. Aggregation of rumors is not allowed, which means
that each node may transmit at most one rumor in one step.
  We focus on networks with tree topologies, that is we assume that the network
is a tree with all edges directed towards the root, but, being ad-hoc, its
actual topology is not known. We provide two deterministic algorithms for this
problem. For the model that does not assume any collision detection nor
acknowledgement mechanisms, we give an $O(n\log\log n)$-time algorithm,
improving the previous upper bound of $O(n\log n)$. We also show that this
running time can be further reduced to $O(n)$ if the model allows for
acknowledgements of successful transmissions.
