Consider the following code:
TreeGraph[{Labeled[1, "Color?"], Labeled[2, "Size?"],
Labeled[3, "Shape?"], Labeled[4, "Size?"], Labeled[5, "Watermelon"],
Labeled[6, "Apple"], Labeled[7, "Grape"], Labeled[8, "\!\(\*
StyleBox[\"Size\",\nFontWeight->\"Bold\"]\)\!\(\*
StyleBox[\"?\",\nFontWeight->\"Plain\"]\)"], Labeled[9, "Banana"],
Labeled[10, "Apple"], Labeled[11, "Taste?"], Labeled[12, "Pomelo"],
Labeled[13, "Lemon"], Labeled[14, "Cherry"], Labeled[15, "Grape"]},
{Labeled[1 \[DirectedEdge] 2, "Green"],
Labeled[1 \[DirectedEdge] 3, "Yellow"],
Labeled[1 \[DirectedEdge] 4, "Red"],
Labeled[2 \[DirectedEdge] 5, "Big"],
Labeled[2 \[DirectedEdge] 6, "Middle"],
Labeled[2 \[DirectedEdge] 7, "Small"],
Labeled[3 \[DirectedEdge] 8, "Round"],
Labeled[3 \[DirectedEdge] 9, "Slimness"],
Labeled[4 \[DirectedEdge] 10, "Middle"],
Labeled[4 \[DirectedEdge] 11, "Small"],
Labeled[8 \[DirectedEdge] 12, "Big"],
Labeled[8 \[DirectedEdge] 13, "Small"],
Labeled[11 \[DirectedEdge] 14, "Sweet"],
Labeled[11 \[DirectedEdge] 15, "Sour"]}]
Above codes don't work, But it works when I change the last term like this:
TreeGraph[{Labeled[1, "Color?"], Labeled[2, "Size?"],
Labeled[3, "Shape?"], Labeled[4, "Size?"], Labeled[5, "Watermelon"],
Labeled[6, "Apple"], Labeled[7, "Grape"], Labeled[8, "Size?"],
Labeled[9, "Banana"], Labeled[10, "Apple"], Labeled[11, "Taste?"],
Labeled[12, "Pomelo"], Labeled[13, "Lemon"], Labeled[14, "Cherry"],
Labeled[15, "Grape"]},
{Labeled[1 \[DirectedEdge] 2, "Green"],
Labeled[1 \[DirectedEdge] 3, "Yellow"],
Labeled[1 \[DirectedEdge] 4, "Red"],
Labeled[2 \[DirectedEdge] 5, "Big"],
Labeled[2 \[DirectedEdge] 6, "Middle"],
Labeled[2 \[DirectedEdge] 7, "Small"],
Labeled[3 \[DirectedEdge] 8, "Round"],
Labeled[3 \[DirectedEdge] 9, "Slimness"],
Labeled[4 \[DirectedEdge] 10, "Middle"],
Labeled[4 \[DirectedEdge] 11, "Small"],
Labeled[8 \[DirectedEdge] 12, "Big"],
Labeled[8 \[DirectedEdge] 13, "Small"],
Labeled[11 \[DirectedEdge] 14, "Sweet"], 11 \[DirectedEdge] 15}].
I don't understand why ?