Hi fabien,
here is a very simple example to get you started (it looks ugly, but to study the docs for more options is left to you as an exercise :-)
package require BWidget
set w .t
Tree $w
pack $w
# create root-node
$w insert end root 1 -text "Rootnode"
$w insert end 1 1.1 -text "1.1"
$w...