Added a proposal for Tree.

redo/proposals/tree.md

@@ -0,0 +1,35 @@
+# Tree
+
+Unlike Table, Tree can only store a set of a single data type. (Blame Windows.)
+
+```go
+type TreeData struct {
+	Checked		bool
+	Image		ImageIndex
+	Text			string
+	Children		[]TreeData		// TODO does this need to be *[]TreeData?
+}
+```
+
+(the facilities for Images has yet to be designed)
+
+Tree itself will operate similarly to Table:
+
+```go
+type Tree struct {
+	Control
+	sync.Locker		// with Unlock() refreshing the view
+	Data() *[]TreeData
+	SetHasCheckboxes(bool)
+	SetHasImages(bool)
+}
+```
+
+By default, a Tree only shows the Text field.
+
+A Tree path is just an `[]int` with each element set to the consecutive index in Children. For example:
+
+```go
+i := []int{3, 4, 5}
+value := tree.Data()[i[0]].Children[i[1]].Children[i[2]].Text
+```