Just need to re-organise the logic:
if (CheckHorizontalSide(SourceMember))
{
bool WhetherContains = lsRelationPath.Contains(SourceMember);
if (lblHorizontalMember.Text == DestinationMember)
{
lsRelationPath.Add(lblHorizontalMember.Text);
lblRelationPath.Text = String.Join("-", lsRelationPath);
lblRelationPath.Visible = true;
}
else if (!WhetherContains)
{
lsMemberID1.Clear();
lsRelationPath.Add(lblHorizontalMember.Text);
Find_Route(lblHorizontalMember.Text, DestinationMember);
}
}