Answer: What you describe is usually called a sucker because it is an upright shoot coming from the root of your original tree. Normally these are cut off at ground level as soon as they appear. You've let it grow. It is getting its nourishment from the roots of the original tree. It probably does not have roots of its own. Now you have a decision to make. You can sever the root from the original tree so the new tree takes the root as its own, or you can cut the suckering tree down as you would any other sucker. I can't really advise you because I cannot examine the sucker or the tree or the root system. If your tree is large and has lots of roots, losing the one the sucker is attached to probably won't hurt it. But before you decide, remember that the weeping part of your weeping cherry is grafted onto the trunk. Any suckering growth that comes from the roots of the tree will not have the weeping characteristic - it will be a full sized cherry tree. Best wishes with your decision.
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