Program installed on host is not visible in lx container

Ubuntu 18.04, a number of lx containers running on it.
I am a complete noob in containers, just getting my toes wet.
I installed "tree" utility using apt on the host, thinking that it would be visible in the containers, but it is not.
Do I have to enter each container and install it there? or there is some configuration to tweak, so the utility can be used in containers?
Thanks in advance.