Welcome to NGA,
@jasu !
I have problems with tree roots in my garden as well (I don't have raised beds, just a "regular" garden). Our yard is completely surrounded by trees, and it is quite amazing how far their roots will travel, and how they will take advantage of some cultivated earth. I just keep digging them out and removing them... I hope someone else here will have a better solution for you!
If all else fails, and the roots are too troublesome, you could consider growing your plants in containers rather than in the raised bed.
