Some plants grow either with a single leader, like a tree, or with multiple stems, like a shrub. In the U.S., they are simply described as 'tree or shrub'.

Examples of this usage:

dictionary.reference.com/browse/shrub
Dictionary.com
**The plant grows as a small tree or shrub** and retains moisture behind its bark, making it a valuable ally against dehydration.

www.ba.ars.usda.gov/hb66/fig.pdf
by CH Crisosto - ‎Related articles
**The plant is a tree or shrub** native to Asia Minor, from where it spread into the. Mediterranean region.

https://books.google.com/books?id=gRsYAAAAYAAJ
Robert Wight - 1840 - ‎Plants
**The plant is a tree or shrub with slender terminal branches**, glabrous, the leaves oblong, elliptical, obtuse at the apex, slightly attenuated at the base, gradually ...