ZigBee, a unique communication standard designed for low-rate wireless personal area networks, has extremely low complexity, cost and power consumption for wireless connectivity in inexpensive, portable and mobile devices. The IEEE 802.15.4 protocol is a promising standard for WSN applications because it pays particular attention to energy efficiency and communication overheads. ZigBee uses Ad-hoc On-demand Distance Vector (AODV) and Tree Routing (TR) as a routing protocol. In TR protocol, the packets follow the tree topology for forwarding the data to the sink node even if the sink node is located near to the source node. In this paper, a survey on different tree routing mechanisms used by ZigBee wireless networks are presented.