Dependency Tree

Hi everyone,
I would like to create a dependency tree in excel to show the dependency of certain tasks.
The logic is the following:

• The task Column A must be completed, before the task in column B can be started.
• Each task can have several dependencies to other tasks

Column A	Column B
A.34.02	A.40.00
A.34.02	A.45.04
A.50.25	A.60.20
A.70.50	A.34.02