To test if an HTML tree object represents a root node, test that the Parent property is missing.

Read HTML code from the URL https://www.mathworks.com/help/textanalytics using webread.

url = "https://www.mathworks.com/help/textanalytics";
code = webread(url);

Parse the HTML code using htmlTree.

tree = htmlTree(code);

Test if the parent of tree references an HTML tree.

tf = ismissing(tree.Parent)

tf = logical
   1

Since tree represents the root node of the HTML tree, the value of tree.Parent is missing and the ismissing function returns 1 (true).