My Crepe Myrtles have multiple "baby" plants every year that sprout up around the bottom of the tree. You can dig these sprouts up and transplant them.
I believe you can also lay a lower branch with an off-shoot, on the ground, place a rock or something heavy on it to keep it in contact with the soil. By next spring, you should have a new plant. Most woody plants/shrubs will work this way.
Locate a shoot at the bottom of a mature plant. Take a shove and dig it up in such that you keep some dirt around the shoot (there will be some fine roots in this dirt). Place this into potting soil or plant into the ground. Keep it watered and it will grow.
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