It would be difficult to tell which tree has invaded your sewer line by looking at the roots from the pipe. You may have to locate where the roots have entered the pipe and trace them back to the tree they grew from. Removing the offending tree may not solve your problem though, because roots from another tree may also grow into the pipe if it is broken.
The best solution would be to repair or replace the broken pipe. If water is leaking out of a sewer line, roots will follow the moisture and grow into the pipe. Roots will not enter a sewer line that is not broken and small roots cannot break a properly installed pipe.
By V. Lazaneo, Urban Horticulture Advisor, Emeritus, UC Cooperative Extension, August 2012