# TF tree has two root node

Hi all,

I am building a MIT-RACECAR with ZED stereo camera and Yokuyo LiDar on it. When I visualized the /tf, it showed two trees:

One tree has 1)odom as root, then 2)base_link as second layer and then 3)Laser, Base_footprint, IMU as children of base_link

Another tree has 1)Map as root, then 2)ZED_center as second layer and then 3)ZED left camera and ZED right camera as children of ZED_Center.

I remember that tf can have only one tree, one root node. Then how can I combine the two trees into one?

Thanks,