My lilac tree has a strange growth and I don’t know that to do with it?

Question

It’s a newish small tree; 4ft. At the base, three shoots appeared and grew rapidly. The leaves and stem were completely different, or so they looked to me. I cut them back. Then another has appeared from about halfway up the trunk.
What is it? Why? And how do I stop it?
Thanks

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Answer 1

It looks like your lilac tree was grafted and there are shoots coming out from below the graft. These are suckers from the rootstalk and need to be removed as they can take over the more desirable top of the tree.

https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-sucker-removal-and-tree-sucker-control.htm