How can I get dataTree from the input ?

@RegisterInputParams, I write down this code.

pManager.AddTextParameter("Text", "T", "Text to export", GH_ParamAccess.tree);

and... @SolveInstance,

List<object[]> t = new List<object[]>();

if(!DA.GetDataTree(0, out t));

But it doesn't work :(

What can I do for GetDataTree ?