Tree

The word tree has its origins in the Proto-Indo-European (PIE) root deru (to be firm, solid, steadfast; particularly, in relation to wood, tree, and objects made of wood) and PIE drew-o (tree). PIE deru is also the source of the words true and truth.
 
From these PIE beginnings comes Proto-Germanic trewam, the source of Old Frisian tre, Old Saxon trio, Old Norse tre, and Old English treo, treow (tree, particularly the oak tree; also, timber, wood, beam, log, stake) and Old English treowwyrhta (tree-wright; i.e., carpenter).
 
‘Christmas’ trees have been part of winter festivals since before Christmas. Ancient people recognized and decorated the trees that stayed green during the winter. During the winter solstice Egyptians would celebrate with green palm rushes. During Saturnalia, the Roman celebration of the solstice, homes and temples were decorated with evergreen boughs. The Celts and Vikings celebrated with evergreen boughs, considered symbols of everlasting life.
 
The contemporary tradition of the Christmas tree is believed to have begun in 16th century Germany when people brought evergreen trees into their homes at Christmas and decorated them with candles. German settlers brought this Christmas tree tradition to the US in the mid-18th century. Other groups in the US at this time resisted the decorating of trees, considering it to be non-Christian. However, by the mid to late 19th century, the decorated Christmas tree gradually took root (so to speak) across the US and Britain, particularly given the influence of Queen Victoria and the annual Christmas tree decorating in her family home.  
 
Reference: Online Etymological Dictionary, https://www.etymonline.com/
​