unable to import py_trees_ros

[owais36]

I am experiencing an issue with py_trees_ros where I want to use behaviour trees in python but I am unable to import py_trees_ros modulein python. I have tried to install the relevant ros packages using :
sudo apt install ros-melodic-rqt-py-trees ros- melodic-rqt-reconfigure
and
sudo apt install ros-melodic-py-trees.
I also installed the simple py_trees using:
pip install py_trees == 0.6.9
I am using ubuntu 18.04 and ROS melodic. has anyone experienced a similar issue in this regard

[owais36]

It is not explicitly mentioned in any documentation but
sudo apt-get install ros-melodic-py-trees-ros
solved the problem