Single channel wireless sensor networks may be unreliable when the channel of choice is either unstable or interfered. Previous work has shown that multi-channel solutions could effectively improve network reliability and deliver higher throughput as well. While a number of multi-channel medium access control schemes have been proposed, there are not much work on routing protocol design addressing the unique challenges multi-channel schemes are facing. In this paper we present a multi-channel cross-layer tree routing protocol. Our contribution includes: Adaptive beaconing corresponding to network topology; Beacon-driven, send-data and receive-data driven link quality estimations; and synchronized MAC and routing table management. Our protocol has been implemented on a testbed consisting of 53 nodes deployed in a 5-story building. Experimental results show that our approach provides fast convergence rate, stable topology and over 99.8% data transmission reliability.