diff --git a/nltk/tree/prettyprinter.py b/nltk/tree/prettyprinter.py
index 2ce106e055..24337ae329 100644
--- a/nltk/tree/prettyprinter.py
+++ b/nltk/tree/prettyprinter.py
@@ -75,7 +75,7 @@ def __init__(self, tree, sentence=None, highlight=()):
             leaves = tree.leaves()
             if (
                 leaves
-                and not any(len(a) == 0 for a in tree.subtrees())
+                and all(len(a) > 0 for a in tree.subtrees())
                 and all(isinstance(a, int) for a in leaves)
             ):
                 sentence = [str(a) for a in leaves]
@@ -291,7 +291,7 @@ def dumpmatrix():
                 matrix[rowidx][i] = ids[m]
                 nodes[ids[m]] = tree[m]
                 # add column to the set of children for its parent
-                if m != ():
+                if len(m) > 0:
                     childcols[m[:-1]].add((rowidx, i))
         assert len(positions) == 0