Use a MouseDown or MouseUp event procedure to specify actions that will occur when a mouse button is pressed or released. Unlike the Click and DblClick events, MouseDown and MouseUp events lets you distinguish between the left, right, and middle mouse buttons. You can also write code for mouse-keyboard combinations that use the SHIFT, CTRL, and ALT keyboard modifiers. Use the ItemFromPoint property to get the item from point. Use the ColumnFromPoint property to get the column from point. 

private void MouseDownEvent(object sender,short Button,short Shift,int X,int Y)
{
}

Private Sub MouseDownEvent(ByVal sender As System.Object,ByVal Button As Short,ByVal Shift As Short,ByVal X As Integer,ByVal Y As Integer) Handles MouseDownEvent
End Sub

private void MouseDownEvent(object sender, AxEXTREELib._ITreeEvents_MouseDownEvent e)
{
}

void OnMouseDown(short Button,short Shift,long X,long Y)
{
}

void __fastcall MouseDown(TObject *Sender,short Button,short Shift,int X,int Y)
{
}

procedure MouseDown(ASender: TObject; Button : Smallint;Shift : Smallint;X : Integer;Y : Integer);
begin
end;

procedure MouseDownEvent(sender: System.Object; e: AxEXTREELib._ITreeEvents_MouseDownEvent);
begin
end;

begin event MouseDown(integer Button,integer Shift,long X,long Y)
end event MouseDown

Private Sub MouseDownEvent(ByVal sender As System.Object, ByVal e As AxEXTREELib._ITreeEvents_MouseDownEvent) Handles MouseDownEvent
End Sub

Private Sub MouseDown(Button As Integer,Shift As Integer,X As Single,Y As Single)
End Sub

Private Sub MouseDown(ByVal Button As Integer,ByVal Shift As Integer,ByVal X As Long,ByVal Y As Long)
End Sub

LPARAMETERS Button,Shift,X,Y

PROCEDURE OnMouseDown(oTree,Button,Shift,X,Y)
RETURN

<SCRIPT EVENT="MouseDown(Button,Shift,X,Y)" LANGUAGE="JScript">
</SCRIPT>

<SCRIPT LANGUAGE="VBScript">
Function MouseDown(Button,Shift,X,Y)
End Function
</SCRIPT>

Procedure OnComMouseDown Short llButton Short llShift OLE_XPOS_PIXELS llX OLE_YPOS_PIXELS llY
	Forward Send OnComMouseDown llButton llShift llX llY
End_Procedure

METHOD OCX_MouseDown(Button,Shift,X,Y) CLASS MainDialog
RETURN NIL

void onEvent_MouseDown(int _Button,int _Shift,int _X,int _Y)
{
}

function MouseDown as v (Button as N,Shift as N,X as OLE::Exontrol.Tree.1::OLE_XPOS_PIXELS,Y as OLE::Exontrol.Tree.1::OLE_YPOS_PIXELS)
end function

function nativeObject_MouseDown(Button,Shift,X,Y)
return

The following VB sample prints the cell's caption that has been clicked:

Private Sub Tree1_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
    ' Converts the container coordinates to client coordinates
    X = X / Screen.TwipsPerPixelX
    Y = Y / Screen.TwipsPerPixelY
    Dim h As HITEM
    Dim c As Long
    Dim hit As EXTREELibCtl.HitTestInfoEnum
    ' Gets the item from (X,Y)
    h = Tree1.ItemFromPoint(X, Y, c, hit)
    If Not (h = 0) Then
        Debug.Print Tree1.Items.CellCaption(h, c) & " HT = " & hit
    End If
End Sub

If you need to add a context menu based on the item you can use the MouseUp event, like in the following VB sample ( the sample uses the Exontrol's ExPopupMenu Component ):

Private Sub Tree1_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)
    If (Button = 2) Then
        ' Converts the container coordinates to client coordinates
        X = X / Screen.TwipsPerPixelX
        Y = Y / Screen.TwipsPerPixelY
        Dim h As HITEM
        Dim c As Long, hit as Long
        ' Gets the item from (X,Y)
        h = Tree1.ItemFromPoint(X, Y, c, hit)
        If Not (h = 0) Then
            Dim i As Long
            PopupMenu1.Items.Add Tree1.Items.CellCaption(h, c)
            i = PopupMenu1.ShowAtCursor
        End If
    End If
End Sub

The following VC sample displays the caption of the cell being clicked:

#include "Items.h"

static CString V2S( VARIANT* pv, LPCTSTR szDefault = _T("") )
{
	if ( pv )
	{
		if ( pv->vt == VT_ERROR )
			return szDefault;

		COleVariant vt;
		vt.ChangeType( VT_BSTR, pv );
		return V_BSTR( &vt );
	}
	return szDefault;
}

void OnMouseDownTree1(short Button, short Shift, long X, long Y) 
{
	int c = 0, hit = 0, hItem = m_tree.GetItemFromPoint( X, Y, &c, &hit );
	if ( ( hItem != 0 ) || ( c != 0 ) )
	{
		CItems items = m_tree.GetItems();
		COleVariant vtItem( hItem ), vtColumn( c );
		CString strCaption = V2S( &items.GetCellCaption( vtItem, vtColumn ) ), strOutput;
		strOutput.Format( "Cell: '%s', Hit = %08X\n", strCaption, hit );
		OutputDebugString( strOutput );
	}
}

The following VB.NET sample displays the caption from the cell being clicked:

Private Sub AxTree1_MouseDownEvent(ByVal sender As Object, ByVal e As AxEXTREELib._ITreeEvents_MouseDownEvent) Handles AxTree1.MouseDownEvent
    With AxTree1
        Dim i As Integer, c As Integer, hit As EXTREELib.HitTestInfoEnum
        i = .get_ItemFromPoint(e.x, e.y, c, hit)
        If (Not (i = 0) Or Not (c = 0)) Then
            Debug.WriteLine("Cell: " & .Items.CellCaption(i, c) & " Hit: " & hit.ToString())
        End If
    End With
End Sub

The following C# sample displays the caption from the cell being clicked:

private void axTree1_MouseDownEvent(object sender, AxEXTREELib._ITreeEvents_MouseDownEvent e)
{
	int c = 0;
	EXTREELib.HitTestInfoEnum hit;
	int i = axTree1.get_ItemFromPoint( e.x, e.y, out c,out hit );
	if ( ( i != 0 ) || ( c != 0 ) )
	{
		string s = axTree1.Items.get_CellCaption( i,c ).ToString();
		s = "Cell: " + s + ", Hit: " + hit.ToString();
		System.Diagnostics.Debug.WriteLine( s );
	}
}

The following VFP sample displays the caption from the cell being clicked:

*** ActiveX Control Event ***
LPARAMETERS button, shift, x, y

local c, hit
c = 0
hit = 0
with thisform.Tree1
	.Items.DefaultItem = .ItemFromPoint( x, y, @c, @hit )
	if ( .Items.DefaultItem <> 0 ) or ( c <> 0 )
		wait window nowait .Items.CellCaption( 0, c ) + " " + Str( hit )
	endif
endwith