Using
display: inline
Top Level 1
Sub Level 1.1
Sub Level 1.2
Sub Level 1.3
Sub Level 1.4
Top Level 2
Sub Level 2.1
Sub Level 2.2
Sub Level 2.3
Sub Level 2.4
Sub Level 2.5
Top Level 3
Sub Level 3.1
Sub Level 3.2
Sub Level 3.3
Sub Level 3.4
Top Level 4
Sub Level 4.1
Sub Level 4.2
Sub Level 4.3
Sub Level 4.4
Sub Level 4.5