Tree care question. I have a beautiful River Birch tree. 4 trunks clumped together around 4 years old. 2 of the trunkd (appx 20 feet tall) bend alot--about halfway o ground--especially when wet--and heavy winds. I assume the wood is soft--I'm concerned will break in winter with snow. Will they ever grow upright again. Trunk is appx 5 " diameter. Should I cut them?