QTreeWidgetItem
construct is meant to be passed multiple strings (not a single one):
>>> s = QTreeWidgetItem(['someString', 'otherString'])
>>> print(s.text(0))
someString
>>> print(s.text(1))
otherString
Passing a single string object 'someString'
is like passing a sequence with multiple single-character strings ['s', 'o', 'm', 'e', 'S', 't', 'r', 'i', 'n', 'g']
.
If you want pass a single string, wrap in list or tuple:
s = QTreeWidgetItem(['someString'])