This wonderfully detailed drawing of the gnarled bark of a tree trunk is in the public domain. It was drawn around 1880 as part of a book on learning how to draw. I think it would make a wonderful base for a button tree or other creative work where the tree leaves and branches are made rather than drawn.
This is a number of drawings from William Walker (b. 1821) that he included in his Handbook of Drawing published in 1880.
This image is copyright free and in the public domain anywhere that extends copyrights 70 years after death or at least 120 years after publication when the original illustrator is unknown.